Internodes Farm Field Area (ha) Variety Class Age (mo) Sampled Bored % Bored

Transcription

1 4 CROP PROTECTION 4.1 ENTOMOLOGY Sugar Cane Stalk Borer (Diatraea saccharalis) The sugar cane stalk borer remained the cane pest of most interest in Work continued in monitoring its level of activity, primarily at New Yarmouth, while efforts were sustained at enhancing field population of the imported biological control agent, Cotesia flavipes. Borer Damage A spike in borer damage levels to 17.8% of internodes was recorded at New Yarmouth in At the time of that survey, based on experience following hurricane Gilbert, it was speculated that these high levels may have been an aberration induced by hurricane Ivan in The estate was therefore revisited in 2006 for an assessment of damage following a normal year. Despite 2005 being by no means normal, in that the island was influenced by hurricanes Dennis and Emily in July followed by Wilma in September, recorded damage of 11.05% (range %), Table 4.1, in 2006 was more in keeping with traditional levels (10-12%). Although these results would tend to discredit the hurricane effect it must be added that hurricane Gilbert had a much more severe impact (measured in terms of stalk damage) on New Yarmouth s cane fields than the combined effect of all three hurricanes in More than a third of fields sampled were considered too mixed to be representative of any single variety. This therefore robbed the survey of meaningful assessment of relative varietal susceptibility. Nonetheless, it may be noted that while the very high 28.5% damage was recorded in BJ7465 on Farm 5, the same variety registered only 8.2% damage on Farm 1. This suggests that location may be a stronger influence than variety on damage levels. Table 4.1: Bborer survey, 2006 Summary New Yarmouth Internodes Farm Field Area (ha) Variety Class Age (mo) Sampled Bored % Bored Farm 1 # BJ7938 7R # # Mixed 3R #34/ Mixed 6R # BJ7465 2R # Mixed 2R #70/ Mixed 3R & 5R # BJ8252 5R Sub Tot/Avg Farm 5 # BJ R #46/ Mixed 2R / Mixed BJ8534 1R # BJ7015 4R # BJ7465 2R # Mixed 12R # R # BJ R Sub Tot/Avg Farm 2 # BJ R # BJ8252 2R # BJ8252 2R # BJ8252 1R # Mixed 2R # BJ7938 2R # Mixed 2R # BJ78100 SP Sub Tot/Avg Grand Tot/Avg

2 Field Parasitism Following successful establishment of Cotesia flavipes, the imported parasite of the borer, in 1983, periodic field sampling has been conducted in attempts to measure its survival and success as an additional biological control agent. Prior to introduction of C flavipes, the borer was contained by native larval parasites, Lixophaga diatraeae and Agathis stigmaterus in addition to egg parasites (Trichogramma spp.) and a variety of predators. Larval parasitism then tended to be of the order of 20% with L diatraeae accounting for some 18% and A stigmaterus for about 2%. Subsequent to establishment of C flavipes, there was an initial surge in total parasitism to 37%, in one study, followed by a gradual decline. At its peak, C flavipes had become the dominant species, accounting for 18% of the host as it aggressively competed with L diatraeae which was found in just 5% of borers. However, with time, field populations of C flavipes tended to decrease so that by 2000 this parasite could hardly be found. Meanwhile, native parasite L diatraeae regained its position of dominance and borer parasitism returned to its former level of roughly 20%. Field studies in recent years reveal a sort of see saw relationship between imported parasite and native species with one gaining ascendency over the other at different times. Field collections from Monymusk and New Yarmouth during 2006 showed a sum total of 17.8% larval parasitism, with L diatraeae accounting for 12% and C flavipes 5.8%, Table 4.2. There were two instances at Monymusk when both L diatraeae and C flavipes were found in substantial quantities in the same field (10.9 &13.1% as well as 12.1 & 15.5% respectively). In most other cases one or the other species dominated sometimes to the total exclusion of the other. Thus there was 42.9% parasitism all due to L diatraeae at Springfield. Similarly, all fields sampled at New Yarmouth revealed the presence of only L diatraeae. C Flavipes was in fact found only at Monymusk where in a couple of instances it was the only larval parasite found. Yet the main collection site at Monymusk which yielded the heaviest field populations of C flavipes was at Waterwell Farm which bordered New Yarmouth. There was not a single instance of detection of the other native parasite, A stigmaterus. Table 4.2: Stalk Borer parasitism, New Yarmouth & Monymusk, 2006 Percent Parasitism Sample Site Date # Borers Collected Lixophaga Cotesia Agathis Total Monymusk 10/1/ Monymusk 2/2/ Monymusk 6/2/ Monymusk 9/2/ Monymusk 16/2/ Monymusk 21/2/ Monymusk 6/4/ Monymusk 20/4/ Monymusk 11/5/ Monymusk 16/5/ New Yarmouth 1/6/ New Yarmouth 19/6/ New Yarmouth 22/6/ New Yarmouth 29/6/ New Yarmouth 11/7/ Monymusk 13/7/ Monymusk 27/7/ Springfield 17/8/ Monymusk 5/9/ Monymusk 14/9/ Monymusk 21/9/ Monymusk 3/10/ New Yarmouth 10/10/ Monymusk 24/10/ Monymusk 9/11/ Monymusk 30/11/ Total/Avg

3 Augmentation Given the low levels of C flavipes detected at New Yarmouth, attempts were made to bolster field populations by lab-rearing specimens collected at Monymusk for re-release at New Yarmouth. A host colony of borers, reared on corn cobs in 1-quart ice cream containers, was maintained in the laboratory throughout the year. At the third to fifth instar stage, borers were exposed to parasitism by C flavipes and then individually reared in test tubes. Parasite progeny were released at the adult stage usually in cane fields older than three months. It is known from previous experience that success rate in this biological control process tends to be low and hinges on an element of luck when the initial goal is field establishment. Nonetheless, with the assumption that C flavipes was indeed present, though undetected at New Yarmouth, it was felt that these augmentative releases would at least increase the likelihood of field populations finding mates thus enhancing the capability of the parasite to reassert its presence. West Indian Canefly (Saccharosydne saccharivora) The canefly remained relatively quiescent throughout the year with only minor flare-ups of population in the New Yarmouth, Monymusk and Caymanas areas. From its heyday in the 1950 s and 1960 s the canefly has remained relatively contained in the last three decades, marking the success of an integrated pest management approach. 4.2 WEED CONTROL During the year, weed management demonstrations and trials were set out throughout the industry. These were carried out in support of recommendations to farmers with regard to rates, time of application, and efficacy of herbicides for varied weed conditions. There were also ongoing trials to garner better understanding of some popular herbicides, in order to use them more efficiently. Weed Management Studies Demonstrations to familiarise growers with herbicide cocktails for effective weed control were set out at Buchanan Brothers Farm at Kings Valley (Frome area) where applications were made at pre- and early post-emergence. Treatments at pre-emergence: 1. Dual Gold (metolachlor)2 L/ha + Atranex 2 L/ha (atrazine) 2. Velpar (hexazinone) 750 ml/ha + Karmex 2.25 kg/ha (diuron) Treatments at early post emergence: 1. Krismat (ametryn + trifloxysulfuron) 2 kg/ha 2. Gesapax 3 kg/ha + Weedmaster (2,4-D + dicamba), 1 L/ha 3. Velpar 750ml/ha +Karmex 2.25 kg/ha The prevailing dry conditions were not conducive to fully demonstrating advantages of pre-emergent chemical application. Weed seed germination and seedling establishment was erratic throughout the plots - some sections being exceptionally clean, while others were weedy, hence the average condition of the plots did not represent a normal outcome from herbicide usage. Similar studies to those in the Frome area were done at Content under centre pivot irrigation on the Dry Irrigated Plains of Central Clarendon. The problem weeds in that area - wild pangola (Dichanthium annulatum) and Seymour grass (Andropogon pertusus) were subjected to pre-emergent treatments of a different combination as outlined below: 1. Sencor (metribuzin) 3 kg/ha in variety J Sencor 3 kg/ha + Atranex 2 L/ha in J Dual Gold 2 L/ha + Atranex 2 L/ha in BJ Velpar 750 ml/ha + Karmex 2.25 kg/ha in var J9501 There were good responses from all but one of the treatments. The control level from the Velpar + Karmex treatment was below par for the weed spectrum in this region. Wild pangola and Seymour grass gave good response to metribuzin at pre-emergence with or without broadleaf killer. Metolachlor + atrazine did well at pre-emergence in the presence of adequate supplies of soil moisture. Mixed stands of grass weeds were a serious threat at St. Thomas Sugar. Regular supplies of herbicides were unavailable for the early cultivation season and this led to challenges for post-emergent weed management. Some generic brands of herbicides on the market failed to effect the level of control needed during the boom growth of the cane crop. Demonstrations with asulam against rice grass, (Sorghum sudanense), paragrass (Panicum muticum), and wild pangola were satisfactory. A cocktail of 6 L/ha of 20

4 Terbutrex + 2 L/ha diuron did a good job during the period. At Halley's Farm in Upper Clarendon there were severe problems with ricegrass, and to a lesser extent paragrass and guinea grass (Panicum maximum). Investigations suggested that herbicide rates used were inadequate to deal with the weed pressure on the farm. Weed control demomonstrations were done at mid post-emergence with the following combinations: 1. Asulam 7 L/ha + Weedmaster 1.5 L/ha 2. Sencor 3 kg/ha When evaluated 10 days post-application (dpa), the treatment of Sencor was ineffective against either of the two weed species. The control was no better at 25 d. On the other hand, there was ~90% control in the section treated with Asulam + Weedmaster at the 25d evaluation. Growth Regulation The application of ethephon is a technology used in parts of the cane growing world to regulate growth in many ways. Flowering, tillering, germination, and stalk maturation are but few of the uses. In Jamaica few farms have used it in sugarcane fields. Observations following application often show: Shorter leaves emerge after an ethephon application On stalks, ethephon produces one or two shortened internodes in the active elongation zone In some varieties ethephon promotes swelling of buds on maturing stalks 500 ml/ha showed improved germination of sugarcane setts with relatively better tillering potential Slight yellowing on leaves of some varieties Pic. 4.1: Yellowing and reduced foliage resulting from ethephon application Pic. 4.2: Improved tillering as a result of ethephon application Pic. 4.3: Applying ethephon to setts in furrows before covering 21

5 Studies within the Industry were set up with the following treatments: 1. Control (no spray) ml/ha Ethrel ml/ha Ethrel ml/ha Ethrel Treated sites were: 1. Two fields at Buchanan Brothers Farm at Glasgow, and one field at Western Sugar, in the Frome area, 2. One field at Content, Mid Clarendon under centre pivot irrigation system 3. Two fields at St. Thomas Sugar Co. in the Wet East In one of the fields at St. Thomas Sugar Co., a single rate of 500 ml/ha was applied to seed pieces in the furrow before covering, for comparison with untreated setts. Results No readings were taken from the field in Mid Clarendon because of less than ideal handling of planting materials that mitigated against normal germination in some parts of the plot. In the fields at St. Thomas Sugar no measurements were taken at 30dpa due to the lack of soil moisture in treated fields. At 60 dpa, readings for both height, and number of tillers/m were greater in the untreated section. Continuing into the second and subsequent intervals, the mean height for canes in the section treated with ethephon remained lower than that in the untreated section, Table 4.3, but the number of tillers/m in the section treated with ethephon increased significantly (p <0.018), Table 4.4. The ANOVA test done on the data recorded for stalk heights and population densities taken at setup indicate that there were no statistical differences (p<0.103) between the means of observations recorded from various treated plots. The higher rates of ethephon (750, 1000 ml/ha) reduced growth significantly (p<0.001), Table 4.3. Mild rates of the growth regulator tended to increase growth above the control, but higher rates tended to induce stunting. Mild chlorosis was also observed in plots treated with the chemical. At time of setup leaf lengths were not measured, but were taken at subsequent 20 d intervals. Again the control (no chemical) had statistically longer leaf blades (p<0.001)table 4.5, than the ethephon treated plots at all time intervals. This observation was similar to that reported by the South African Sugar Association, and the Indian Sugarcane Breeding Institute. Conclusions The studies with ethephon indicate strongly that the chemical may be used to improve field stand, especially where germination tends to be less than ideal. The effect however, is not as pronounced as that reported from Texas and India. Its potential to improve germination when applied to the furrow could not be verified and needs more intensive investigation. Retarded early growth is not an outcome farmers would like, especially with the challenges of weed pressures and moisture stress. Tiller attrition at stalk formation stage as observed in treatment plots diminished early gains, and may only be important where germination is less than ideal. Table 4.3: Mean stalk heights (mm) of BJ78100 at 60 d, then at 20 d intervals, after ethephon treatment on seed pieces before covering, St. Thomas Sugar Co Interval Treated Untreated SED Prob Table 4.4: Mean tiller counts (#/m) of BJ78100 at 60 d, then at 20 d intervals, after ethephon treatment on seed pieces before covering, St. Thomas Sugar Co Interval Treated Untreated SED Prob Table 4.5: Summary of Experiment II - ethephon treatment on foliage after germination, St. Thomas Sugar Co Parameter Control Ethephon SED Prob Plant height (mm) Leaf length (mm) Tiller density (#/m)