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R. E. C o l e m a n , Plant P h y s i o l o g i s t , Crops Research D i v i s i o n , Agricultural Research S e r v i c e , United S t a t e s Department of Agriculture
Among the most i n t e r e s t i n g plant growth s t i m u l a n t s t h a t h a v e b e e n d i s c o v e r e d are t h e g i b b e r e l l i n s . Although t h e s e s u b s t a n c e s w e r e known t o t h e J a p a n e s e a s early a s 1926, i t w a s not until r e c e n t l y t h a t t h e y a t - t r a c t e d the a t t e n t i o n of plant p h y s i o l o g i s t s in the United S t a t e s . The g i b b e r e l l i n s are s u b s t a n c e s produced by t h e fungus, G i b b e r e l l a fujikuroi, which c a u s e s a d i s e a s e of r i c e , and at p r e s e n t t h e r e are at l e a s t two of t h e s e g i b b e r e l l i n c o m p o u n d s , g i b b e r e l l i c acid and g i b b e r e l l i n A. Many growth stimulatory phenomena have b e e n a t t r i b u t e d to t h e s e c o m p o u n d s . The most obvious is t h a t of elongation of i n t e r n o d e s . Other r e s p o n s e s h a v e b e e n p a r t h e n o c a r p i c fruit development in tomato and e a r l i e r flower- ing in s e v e r a l p l a n t s (1); t h e replacement of the cold requirement for flowering in c e r t a i n p l a n t s (2); r e s t o r a t i o n of normal growth to dwarf mutant maize p l a n t s (3); and t h e breaking of dormancy in many p l a n t s . The r e c e n t l i t e r a t u r e a c t u a l l y c o n t a i n s hundreds of r e f e r e n c e s to other growth effects upon specific p l a n t s . The l i t e r a t u r e through 1956 h a s b e e n a d e q u a t e l y reviewed by Stowe and Yamaki (6). More r e c e n t l y , monographs have b e e n prepared by producers of g i b b e r e l l i n compounds (7) (8).
1The g i b b e r e l l i c a c i d u s e d in t h i s study w a s most g e n e r o u s l y supplied by Dr. John D. Garber of M e r c k , Sharpe and Dohme; Mr. H.
F, S e e l a n d of S. B. Penick and C o . ; and Mr. L. F. Bewick of Vesicol C h e m i c a l C o r p o r a t i o n .
125
This report covers only effects of g i b b e r e l l i c a c i d on s u g a r c a n e as observed in experiments conducted at the U. S. Sugarcane Field Station at Houma, L o u i s i a n a . There is a report from Puerto Rico (4) of t h e effects of g i b b e r e l l i n on s u g a r c a n e . Workers t h e r e s o a k e d s u g a r c a n e s e e d p i e c e s in s o l u t i o n s of various c o n c e n t r a t i o n s of g i b b e r e l l i c a c i d . Follow- ing such t r e a t m e n t s they reported i n c r e a s e s in growth of from 4 0 to 100 per c e n t . Similarly, reports from Hawaii (5) h a v e shown that g i b b e r e l l i c acid solution applied to the spindle of s u g a r c a n e p l a n t s c a u s e d a 50 per cent i n c r e a s e in height as compared with u n t r e a t e d p l a n t s . Bourne (7) has reported similar growth effects and an i n c r e a s e in rate of germination of s e e d p i e c e s following a dip in g i b b e r e l l i c acid s o l u t i o n s .
The s t u d i e s reported in t h i s paper followed s e v e r a l l i n e s of i n v e s t i - g a t i o n . In g r e e n h o u s e experiments t h e effects of g i b b e r e l l i c a c i d as s e e d piece treatment and as a foliar spray on young p l a n t s w e r e s t u d i e d . In the field the g r o s s effects of r e p e a t e d foliar s p r a y s upon growth and yield were s t u d i e d . G i b b e r e l l i c acid w a s a l s o applied in t h e field as a p r e - harvest t r e a t m e n t , and i t s effect upon s u c r o s e c o n t e n t of s u g a r c a n e for milling m e a s u r e d . Since some of t h e s e t e s t s and r e s u l t s of other workers (9) have shown that t h e g i b b e r e l l i n s are able to promote growth in cool w e a t h e r , the effects of foliar s p r a y s upon growth in t h e field during November were s t u d i e d .
In one of t h e s e experiments s i n g l e eye s e e d p i e c e s were t r e a t e d by soaking for 5 hours in s o l u t i o n s containing v a r i o u s amounts (5 and 10 ppm) of g i b b e r e l l i c a c i d . The c u t t i n g s were then i n c u b a t e d and p l a n t e d in
4 - i n c h pots in the g r e e n h o u s e . Another lot of s e e d p i e c e s w a s t r e a t e d by applying a 1000 ppm lanolin p a s t e of g i b b e r e l l i c a c i d to the nodal z o n e . Varieties C . P . 4 4 - 1 0 1 and C . P . 44-155 w e r e u s e d i n t h e s e t e s t s , 100 p l a n t s being u s e d for each treatment. The effect of the g i b b e r e l l i c acid t r e a t m e n t s upon the height of the p l a n t s is shown in Figure 1. In Figure 1 the a v e r a g e height of all the t r e a t e d p l a n t s is compared to the a v e r a g e height of the control plants for C . P . 4 4 - 1 0 1 . The growth patterns for the p l a n t s of C . P . 44-155 were e s s e n t i a l l y the same as t h o s e shown in Figure 1. The w e e k l y height measurements did not show significant differences b e t w e e n the various c o n c e n t r a t i o n s of g i b b e r e l l i c a c i d u s e d in t h i s t e s t . For the period up to 23 days after t r e a t m e n t , t h e t r e a t e d p l a n t s i n c r e a s e d in h e i g h t , On an a v e r a g e , at a 56 per cent g r e a t e r rate t h a n the control p l a n t s . After t h i s period t h e r a t e of growth of the t r e a t e d p l a n t s appeared to l e v e l off while that of t h e control p l a n t s continued at t h e same r a t e . By t h e 47th day after treatment t h e r e w a s very l i t t l e difference in t h e r a t e s of growth b e t w e e n the t r e a t e d and con- trol p l a n t s , although t h e t r e a t e d p l a n t s w e r e t a l l e r . At t h i s s t a g e of growth a group of t h e p l a n t s from e a c h treatment w a s sprayed with a 10 ppm g i b b e r e l l i c a c i d s o l u t i o n . This treatment r e s u l t e d in a s e c o n d i n c r e a s e in rate of growth over that of the previous t r e a t m e n t s ( s e e Figure 1). However, 21 days after t h i s s e c o n d t r e a t m e n t , t h e rate of growth of all the t r e a t m e n t s w a s nearly the s a m e . S u b s e q u e n t spray t r e a t m e n t s w e r e given at 21-day i n t e r v a l s to the same groups of p l a n t s . These r e p e a t e d t r e a t m e n t s carried through 112 days produced 60 per
cent t a l l e r t h a n t h e control p l a n t s .
The p l a n t s which w e r e t r e a t e d only by soaking in g i b b e r e l l i c acid solutions were h a r v e s t e d 112 days after treatment and height and weight measurements o b t a i n e d . These r e s u l t s are summarized in Table 1. After t h i s period of growth t h e r e w e r e no significant differences in height due t o the g i b b e r e l l i c acid t r e a t m e n t s . With variety C . P . 4 4 - 1 0 1 , there were significant differences in t h e fresh weight of the p l a n t s . Hence while the single a p p l i c a t i o n of g i b b e r e l l i c acid as a s e e d - p i e c e t r e a t -
ment c a u s e d more rapid elongation in the earlier s t a g e s of growth, it also r e s u l t e d in more spindly p l a n t s . This is reflected in the data of Table 1 which show that the untreated p l a n t s of C . P . 4 4 - 1 0 1 had a significantly greater fresh w e i g h t . When g i b b e r e l l i c acid is applied repeatedly it affects t h e p l a n t s by an i n c r e a s e in both height and w e i g h t .
Table 1. Effect of soaking s e e d p i e c e in g i b b e r e l l i c acid s o l u t i o n s of v a r i o u s c o n c e n t r a t i o n s for 5 hours upon t h e height and fresh weight of two v a r i e t i e s of s u g a r c a n e .
Treatment 5 ppm G. A.
10 ppm G . A.
1000 ppm l a n o l i n Water
Untreated
paste
Average height (cms .) C . P .
4 4 - 1 0 1 3 1 . 4 3 4 . 3 3 6 . 4 3 3 . 8 3 3 . 5
C . P . 44-155
3 0 . 2 3 0 . 0 2 9 . 7
- -
Average fresh W t . (gms.) C . P .
4 4 - 1 0 1 3 5 . 9 3 8 . 5 4 4 . 2 5 1 . 8 4 9 . 4
C . P . 44-155
3 3 . 5 3 2 . 6 3 7 . 0
- -
n . s . n . s . LSD .05 = 1.2 n . s .
In field e x p e r i m e n t s , foliar sprays of g i b b e r e l l i c acid were applied to p l a n t s of variety C . P . 4 4 - 1 0 1 in 1 2 - f t . x 1 5 - f t . r e p l i c a t e d p l o t s . These a p p l i c a t i o n s w e r e r e p e a t e d at 10-day i n t e r v a l s throughout t h e growing s e a s o n from April 19 to October 4, 1957. When t h e p l a n t s w e r e y o u n g , s o l u t i o n s of 10 ppm were applied and as t h e p l a n t s became larger t h e c o n c e n t r a t i o n w a s i n c r e a s e d to 2 0 , 4 0 , 5 0 , 7 0 , and 100 ppm. The a p p l i c a t i o n r a t e w a s 100 g a l l o n s per a c r e . Growth measurements of individual p l a n t s were t a k e n at regular i n t e r v a l s during the growing s e a s o n . The r e s u l t s of t h e s e measurements are plotted as the mean height of t h e p l a n t s in F i g . 2, and as i n c r e m e n t s of growth in F i g . 3.
The data p r e s e n t e d in F i g . 2 show t h e cumulative effect of t h e smaller growth i n c r e a s e s upon t h e t o t a l height of t h e p l a n t s at h a r v e s t . It a l s o shows the greater rate of growth of t h e t r e a t e d compared to the u n t r e a t e d p l a n t s during t h e months of September and O c t o b e r . In F i g . 3, where the periodic growth increments are p l o t t e d , s e v e r a l i n t e r e s t i n g r e s u l t s are e v i d e n t . During the early growth p e r i o d , April 19 to June 17, when rainfall w a s about a v e r a g e and mean t e m p e r a t u r e s w e r e normal, the t r e a t e d p l a n t s showed a o n e - i n c h i n c r e a s e in height over the untreated p l a n t s for each p e r i o d . During t h e period June 17 to 28, t h e t r e a t e d p l a n t s i n c r e a s e d in height two and o n e - h a l f i n c h e s more than t h e control p l a n t s . Rainfall w a s sufficient during t h i s period but mean t e m p e r a t u r e s w e r e s e v e r a l d e g r e e s below n o r m a l . The g r e a t e s t growth difference b e t w e e n t r e a t e d and u n t r e a t e d p l a n t s ( 4 . 5 i n c h e s ) occurred b e t w e e n the period June 28 to July 23 .
During t h i s period there w a s a c t u a l l y a rather s e v e r e drought with no rainfall from June 28 to July 17, and soil moisture l e v e l s at 18-inch depth a c t u a l l y dropped to 18 per cent a v a i l a b l e m o i s t u r e . During t h e next 2 0 - d a y growth interval the untreated p l a n t s showed a greater in- c r e a s e in height than the t r e a t e d p l a n t s . This period w a s marked by sufficient rainfall and maximum mean t e m p e r a t u r e s which are c h a r a c - t e r i s t i c of t h e growth peak r e a c h e d each s e a s o n . As mean t e m p e r a t u r e s began to d e c l i n e during the period August 26 to October 16, once again the gibberellic acid t r e a t e d plants showed significant i n c r e a s e s in height over the control p l a n t s .
The data obtained on h a r v e s t i n g t h i s experiment are shown in Table 2, t e s t A. Determinations were made of stalk h e i g h t , w e i g h t , and d i a m e t e r , length of millable c a n e , number of n o d e s , length of n o d e s , and yield of millable c a n e . The j u i c e w a s a n a l y z e d for t o t a l s o l i d s and s u c r o s e . Since floral i n i t i a t i o n occurred during t h i s s e a s o n o b s e r v a t i o n s were made as to the p e r c e n t a g e of flowering in t h e two t r e a t m e n t s . As is i n d i c a t e d in t h e data of Table 2, although the r e p e a t e d g i b b e r e l l i c acid t r e a t m e n t s produced p l a n t s with an overall i n c r e a s e in height of 31 i n c h e s over the control p l a n t s , there w a s a c t u a l l y only a 10-inch in- c r e a s e in length of millable c a n e . Stalk w e i g h t , stalk d i a m e t e r , number of n o d e s , length of internode, and yield in t o n s of c a n e per a c r e , were not significantly affected by the g i b b e r e l l i c acid t r e a t m e n t s . The j u i c e a n a l y s e s showed no significant e f f e c t s , nor w a s there any effect upon floral i n i t i a t i o n .
Another experiment w a s carried out to determine the effect of date of application of gibberellic acid upon yield and j u i c e quality of s u g a r c a n e . Starting in l a t e August, additional plots of sugarcane plants which had not b e e n t r e a t e d previously were sprayed with 100 ppm gibberellic acid solution at 10-day i n t e r v a l s . Various plots received 5, 3, 2, and 1 such treatment prior to harvest data from t h i s experiment are shown in Table 2, t e s t B. In t h i s t e s t there w a s a significant effect in the overall height of the plants receiving five foliar a p p l i c a t i o n s of gibberellic a c i d . The plot which received a single treatment six days before harvest showed a significant i n c r e a s e in sucrose content of t h e j u i c e . However, since t h i s is a single observation the d e s i r a b i l i t y of continued i n v e s t i g a t i o n of this phenomenon is i n d i c a t e d .
In view of the evidence above in which it appeared that foliar a p p l i c a t i o n s of gibberellic acid produced greater i n c r e a s e s in height of sugarcane p l a n t s when environmental conditions were unfavorable for normal growth, two-month old p l a n t s , variety C . P . 4 4 - 1 0 1 , were treated in the field during November. In t h i s t e s t two foliar applica- t i o n s of a 20 ppm gibberellic acid solution were made at an 1 1 - d a y i n t e r v a l . The t e s t terminated with a killing freeze 15 days after the second a p p l i c a t i o n . During this period the average maximum temperature w a s 68°F, and the average minimum temperature 51° F. The r e s u l t s of growth measurements t a k e n at two intervals during t h i s t e s t are tabu- lated below:
Period Growth in Inches Treated Control November 6 to November 17 2 . 5 0.60 November 17 to December 2 2 . 1 0.8 0
Check
G.A. Spray - 100 ppm 1. 5 times * before harvest G.A. Spray - 100 ppm
2. 3 times * before harvest G.A. Spray - 100 ppm
3. 2 times * before harvest G.A. Spray - 100 ppm
4. 1 time * before harvest G.A. Spray - 100 ppm
5. 1 time * before harvest Check
* 1 . Sprays applied 8 / 2 6 , 9 / 5 , 9 / 1 6 , 9/25 and 10/4/57 2. Sprays applied 9 / 1 6 , 9/25 and 10/4/57
3. Sprays applied 9/25 and 10/4/57 132 4.' Spray applied 10/4/57
5. Spray applied 10/11/57 G.A. Spray 10, 40, & 50 ppm
10-day intervals 4/19 to 10/4/57
Variety C . P . 44-101 plant c a n e , Ashland Plantation, Houma, La. Harvested October 17, 1957.
These r e s u l t s rather clearly i n d i c a t e the pronounced effect of gibberellic acid in increasing the height of p l a n t s during periods in which cool temperatures greatly retard the growth of control p l a n t s . Another p o s s i b i l i t y s u g g e s t e d by such r e s u l t s is that gibberellic a c i d may in part replace the long day requirement for v e g e t a t i v e growth, as s u g g e s t e d by Lockhart (10). Previous workers (2, 11) have shown that gibberellic acid h a s replaced the long day requirement for flowering.
SUMMARY
Several experiments were performed to a s c e r t a i n the effect of gibberellic a c i d on the growth of s u g a r c a n e . In greenhouse t e s t s it w a s found t h a t s e e d - p i e c e treatments i n c r e a s e d the height of p l a n t s 56 per cent for a period up to 23 d a y s . After t h i s period the rate of growth of t r e a t e d plants appeared to l e v e l off while that of control p l a n t s con- tinued at the same r a t e . At harvest 112 days after treatment there were no significant differences in height due to the gibberellic acid treat- m e n t s . There w e r e , however, significant differences in fresh weight of the plants at h a r v e s t , the untreated p l a n t s having a greater weight than the t r e a t e d p l a n t s .
Repeated foliar application of a 10 ppm gibberellic acid solution applied to plants in the greenhouse produced plants which were 60 per cent t a l l e r and with a significantly greater fresh weight than control p l a n t s .
Experiments in the field with repeated foliar a p p l i c a t i o n s of
gibberellic acid solutions for a 6-month growth period produced plants 30 i n c h e s t a l l e r than control p l a n t s . However, harvest data i n d i c a t e d that such treatments produced only 10 i n c h e s greater length of millable s t a l k s . The gibberellic acid treatments did not affect the ultimate yield of tons of sugarcane per a c r e , stalk weight or diameter, number of nodes or length of i n t e r n o d e s , total s o l i d s , s u c r o s e , or j u i c e purity.
There w a s evidence from growth measurements t a k e n throughout the growth period that gibberellic acid had a more pronounced effect upon height of plants when environmental conditions were unfavorable for normal v e g e t a t i v e growth. Growth measurements obtained during the extremely cool conditions of November showed that gibberellic acid treatments i n c r e a s e d the height of plants three times that of c o n t r o l s .
LITERATURE CITED
(1) W i t t n e r , S. H . , M. J. Bukovac, H. M. S e l l , and L. E. W e l l e r . Some effects of gibberellin on flowering and fruit s e t t i n g . Plant P h y s i o l . 3 2 : 1 , 3 9 - 4 1 . 1957.
(2) Lang, A. Bolting and flowering in biennial Hyoscyamus niger, induced by g i b b e r e l l i n . Plant P h y s i o l . 3 1 : S u p p . 1, XXXV. 1956.
(3) Phinney, B. O. Growth r e s p o n s e of s i n g l e - g e n e dwarf mutants i n maize t o gibberellic a c i d . P r o c . N a t l . Acad. S c i . , U . S . 42: 1 8 5 - 1 8 9 . 1956.
(4) Chardon, C. B. G i b b e r e l l i n , a new plant growth activating sub- s t a n c e . Annual Meeting of the Association of Sugar Technicians of Puerto Rico, San Juan, P. R. 1956.
(5) H. S. P. A. Experiment Station Comm. Report. 1956, 1 1 - 1 2 . (6) Stowe, B. B . , and T. Yamaki. The history and p h y s i o l o g i c a l action
of the g i b b e r e l l i n s . Ann. Rev. Plant P h y s i o l . 8: 1 8 1 - 2 1 6 . 1957, (7) Anon. Gibrel prepared by Merck & C o . , I n c . 44 p p . 1957.
(8) Anon. Abstracts of Current Research on the effects of gibberellic acid o n p l a n t s . Velsicol Chemical C o r p . Bulletin N o . 5 1 2 - 3 . 1957.
(9) W i t t w e r , S. H . , and Bukovac, M. J. Gibberellin and higher p l a n t s : V. Promotion of growth in g r a s s at low t e m p e r a t u r e s . M i c h . State U n i v . Agr. Expt. S t a . Q u a t . Bull. 39(4): 6 8 2 - 8 6 . 1957.
(10) Lockhart, J. A . , and J. Bonner. Effects of gibberellic acid on photoperiod-controlled growth of woody p l a n t s . Plant P h y s i o l . 32: 5 . 4 9 2 - 9 7 . 1957.
(11) Wittwer, S. H . , and M. J. Bukovac. Gibberellins - new chemicals for crop production. Agr. Expt. S t a . M i c h . Q u a t . Bull. 4 7 . 1957.
OF THE SUGAR CANE BORER A. L. D u g a s , Entomologist Dugas Pest C o n t r o l , Incorporated
Baton Rouge, Louisiana
The chemical control of the sugar c a n e borer by the u s e of an in- s e c t i c i d e should be considered as an immediate control for an infestation at a cost l e s s than the expected l o s s in c a n e . This means that the toxicity of an i n s e c t i c i d e is only one of s e v e r a l factors to be t a k e n into consideration in deciding on i t s u s e , and c e r t a i n principles must be understood and weighed if effective and economical control over a period of y e a r s is to be obtained by the u s e of i n s e c t i c i d e s and other control measures .
W e , as Sugar Cane T e c h n o l o g i s t s , must concern o u r s e l v e s with t h e s e t e c h n o l o g i c a l principles of the borer problem in order to evaluate recommendations and apply them properly. Certain q u e s t i o n s come to mind when d r a s t i c changes in recommendations for a sugarcane borer control program are made; namely,
1. With limited d a t a , is it w i s e that the main sugar cane growing area of Louisiana be plunged into an organic i n - s e c t i c i d e program with i t s p o s s i b l e limitations and c o n - s e q u e n c e s , as shown by e x t e n s i v e data on sugar cane and programs with other crops ?
2 . Should r y a n i a , with i t s specific u s e s and a d v a n t a g e s , s u p - ported by many years of research d a t a , field t e s t i n g , and practical a p p l i c a t i o n , be dropped in favor of an "all out"
program b a s e d on an organic i n s e c t i c i d e , endrin?
136
3. What is the b a s i s for such an untimely statement concerning the effectiveness of Trichogramma p a r a s i t e s , d e s p i t e s e v e n years of e x h a u s t i v e research by H i n d s , Spencer,
Osterburger and others and upon which the recommendation for their u s e by the Louisiana State University h a s b e e n b a s e d for 30 y e a r s ?
4. What are the limiting factors in obtaining the most effective control of the sugar cane borer with i n s e c t i c i d e s ?
The a n s w e r s to t h e s e q u e s t i o n s , b a s e d on an understanding of the principles a s s o c i a t e d with the problem, and r e p r e s e n t a t i v e data to support c e r t a i n c o n c l u s i o n s are given b e l o w .
I. Recommended Applications Should be Limited to Sugar Cane Acreage with a Borer Infestation Justifying the Monetary Expenditure.
Chemical control should be resorted to only where the proper checking of fields r e v e a l s the borer infestation in a general area to be sufficiently heavy to justify the c o s t . It should then be done right or not at a l l .
The sugar cane industry now enjoys t h e enviable position that many farms and a l s o certain a c r e a g e on most farms do not have a severe borer i n f e s t a t i o n . This highly favorable position c a n be maintained only through the conservation of the natural enemies of t h e b o r e r .
In a normal y e a r , only about one-half of the cane a c r e a g e h a s a borer infestation which j u s t i f i e s the u s e of i n s e c t i c i d e s . With r y a n i a , the material now being u s e d by t h o s e in a chemical control program, the growers who are not dusting profit by t h o s e who are b e c a u s e of the fact that many of t h e h e a v i e s t infestations are controlled and spread to l e s s
severely infested fields is p r e v e n t e d . The general u s e of an organic i n s e c t i c i d e , such as endrin, might c a u s e a general i n c r e a s e in infestation on all p l a c e s , eventually making it necessary that i n s e c t i c i d e s be used on all cane a c r e a g e or heavy borer l o s s e s be a b s o r b e d .
The Bunkie area is a good example of what the e x t e n s i v e u s e of organic i n s e c t i c i d e s may d o . There w a s no borer problem in the area prior to the g e n e r a l u s e of organics on c o t t o n . Today, t h e problem is many times greater in the Bunkie area than in the main part of t h e sugar cane a r e a . The i d e n t i c a l thing happened on Allendale P l a n t a t i o n , in West Baton Rouge P a r i s h , in all c a n e a c r e a g e within a fifty acre radius of a hundred care block of c o t t o n .
With an i n s e c t i c i d e such as r y a n i a , one or more a p p l i c a t i o n s may be a p p l i e d , and then applications d i s c o n t i n u e d without fear of i n c r e a s i n g borer i n f e s t a t i o n . Based on all a v a i l a b l e data t h i s cannot be done with an organic i n s e c t i c i d e .
I I . An Early S e a s o n Program of I n s e c t i c i d a l Application
In an early s e a s o n program of i n s e c t i c i d a l c o n t r o l , the long period of time e l a p s i n g from the l a s t a p p l i c a t i o n of poison to harvest time p r e s e n t s certain r i s k s of reinfestation and thereby n e c e s s i t a t e s more complete treatment of infested a r e a s . This fact i n c r e a s e s the importance of the destruction of natural enemies of the borer by an organic i n s e c t i c i d e .
A first generation control program w a s p o s s i b l e under conditions
which e x i s t e d at one t i m e , when heavy borer infestations were more l o c a l i z e d . In this c a s e , s u c c e s s depends upon a near complete d e s t r u c - tion over a wide area of the first g e n e r a t i o n , which actually does no damage measurable at harvest t i m e , so that the population of succeeding g e n e r a t i o n s , which do the damage will not be sufficiently heavy to c a u s e injury. There are u s u a l l y no joints on the plant at the time of the first generation so that protection of t h e plant is of no particular v a l u e .
The d i s t i n c t hazard involved in t h i s p h a s e of control is t h e p o s s i b i l i t y of reinfestation by later g e n e r a t i o n s . It is therefore n e c e s - sary that a large part of the infested area be t r e a t e d so as to l e s s e n the likelihood of an influx of moths from adjoining untreated cane or c o r n .
In second generation control, protection is given to the lower five to seven joints of the cane plant so that benefits obtained are measurable at h a r v e s t t i m e . Although injury from later generations are l e s s likely to completely e r a s e the benefits more effective control at harvest is dependent upon a sufficiently high kill of the second generation of borers so that there will be a minimum r e i n f e s t a t i o n . Actually, extending the period of protection to include second and third generations is highly a d v i s a b l e .
In future y e a r s , it may be a d v i s a b l e to go back to a first genera- tion i n s e c t i c i d e program, if borer infestations should again become more l o c a l i z e d through t h e u s e of r e s i s t a n t v a r i e t i e s and higher kill of over- wintering borers by more severe w i n t e r .
III. Young Borers Must be Killed Before they Enter the Plant and t h e Required Number of Applications be Applied.
The proper timing of chemical a p p l i c a t i o n s is very important for effective control s i n c e the degree of kill after the young borers enter the plant is rather insignificant.
A general recommendation on the number of a p p l i c a t i o n s to be used on a p l a c e cannot p o s s i b l y take into account the actual need of a l e s s e r or greater number of a p p l i c a t i o n s for a specific s i t u a t i o n . It is generally understood that four a p p l i c a t i o n s are not actually n e c e s - sary on much of the cane acreage in Louisiana and if applied, r e s u l t s only in added expense with no economic gain in degree of c o n t r o l . O n e , t w o , t h r e e , four or even more a p p l i c a t i o n s may be required depending upon the occurrence and development of the borer infestation in a particular field. In many i n s t a n c e s only the first or second applica- tion is sufficient to bring an infestation under c o n t r o l . It is only with a material like r y a n i a , which does not destroy natural e n e m i e s , that one can discontinue a p p l i c a t i o n s without fear of being eaten up by borer by harvest t i m e .
So, under such c o n d i t i o n s , an organic could not be s u b s t i t u t e d for ryania even though it w a s proven that it would result in a higher degree of control if four a p p l i c a t i o n s of each were a p p l i e d . This does not t a k e into account the probable c o n s e q u e n c e s in future y e a r s . There i s , therefore, a definite p l a c e for ryania in the chemical program even though the u s e of endrin or some other organic would be a d v i s a b l e .
IV. Extending the Control Period by Poisoning the Third Generation of Borers.
Control of second generation borers is not always sufficient in some fields of cane to produce the overall control d e s i r e d . In most y e a r s t h e injury inflicted by third generation borers is of no real con- s e q u e n c e , e s p e c i a l l y if Trichogramma p a r a s i t i s m has reached a high l e v e l . However, there are always c e r t a i n fields in which extending the control period by treating for third generation infestations is highly d e s i r a b l e . This is e s p e c i a l l y true in stunted c a n e , which is subject to the same type of injury as that inflicted by the second generation to cane of normal growth.
On a farm where s u c c e s s f u l second generation control h a s been a c c o m p l i s h e d , except in stunted c a n e as described a b o v e , only one or two a p p l i c a t i o n s are usually required to protect l o c a l i z e d a r e a s from third generation a t t a c k . This may often be the answer to some d i s s a t i s - faction as to t h e ultimate control over an entire p l a c e . There are known i n s t a n c e s where four u n n e c e s s a r y a p p l i c a t i o n s are made to control the second g e n e r a t i o n , whereas one or two on the third would have resulted in greater g a i n s .
The r e s u l t s of two r e p r e s e n t a t i v e t e s t s , one conducted on Georgia Plantation of South Coast Company and the other on W i l k i n s o n ' s Poplar Grove Plantation, shows comparable gains that can be expected from second and third generation c o n t r o l , and t h e manner in which insecticidal
control a l t e r s the location of borer infestation on the s t a l k . It is quite evident that the sugarcane plant is able to w i t h s t a n d a c o n s i d e r a b l e degree of top joint infestation with comparatively l i t t l e d a m a g e .
Graphs 1 and 2 depict the borer infestation as measured by the percentage of each joints bored in the summer and at harvest t i m e , and Tables 1 and 2 give the i n c r e a s e s in per cent s u c r o s e and purity and in yields of cane and sugar from the control of the various genera- tions of b o r e r s . An examination of the graphs gives a picture of the borer infestation by individual j o i n t s . The wide spread between infesta- tion l i n e s in the summer (graph (No. 1) are brought c l o s e r together by reinfestation and by third and fourth generation borer a t t a c k , thus showing a different picture in the harvest time g r a p h . Graph 2 a l s o shows how Trichogramma and other natural enemies reduce borer i n f e s t a t i o n s as the s e a s o n p r o g r e s s e s , since there is a decided d e c r e a s e in bored joints l a t e in the s e a s o n . The fact that second generation control protected the lower j o i n t s , allowed the plants to grow and produce millable s t a l k s in spite of having 36 percent of the joints bored at harvest t i m e . With only 3 percent difference in per cent j o i n t s bored at h a r v e s t , a gain of 6.67 t o n s and 1384 l b s . of sugar r e s u l t e d from 2nd generation control as compared to 1.20 tons and 562 l b s . of sugar from the control of only the third g e n e r a t i o n , as shown in Table 1. The gains from controlling both generations is far from being what would be expected according to the differences in per cent j o i n t s b o r e d . It is obvious from t h e s e data that the cane plant can w i t h s t a n d high infesta- tions of borers in the top j o i n t s .