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Tuesday, August 15, 2017

West Texas Cotton: Scout for Aphids and Bollworms

Suhas Vyavhare, Extension Cotton Entomologist, Texas A&M AgriLife Extension Service


Cotton will benefit from some of the timely rainfall we have been receiving recently. However, it is going to make conditions better for survival and multiplication of several pest species as well. In general, the hot and dry weather of West Texas helps to keep bollworm numbers in check (through desiccation of eggs). Humid and cloudy conditions over the last couple of weeks, however, may increase egg hatch rate and worm survival in cotton. In addition, added new growth on plant terminals will help both bollworms and aphids thrive better.

Over the last 10 days, we have spotted many fields with cotton aphid infestations. Aphid colonies are mainly concentrated to plant terminals but as the numbers build-up, they may move on to the leaves. Overall, beneficial numbers seem to be lower compared to the previous year, but they are present. Isolated showers will also help wash out honeydew and some of the aphids from the plants. If aphid colonies are spotty and mostly restricted to plant terminals, I would wait and monitor the situation over the next few days. Often aphid populations crash out in response to beneficials and rain. Click the link below to access more detailed information on cotton aphids: http://lubbock.tamu.edu/files/2017/07/Cotton-aphid_ENTO074.pdf

I have also come across a few reports of bollworm damage to non-Bt cotton. In our research trials, bollworm damage ranges from 5-6% boll injury in non-Bt cotton and <1% in Bt cotton. The threshold is 6% fruit injury with the presence of live worms in both Bt and non-Bt crop. Among various insecticide options for bollworm control, Diamide insecticides (Prevathon and Besiege) are the most reliable choices. Remember, Besiege contains both a diamide and a pyrethroid so it would be a better choice if stink bugs are present too. However, if aphid colonies are present in the field, the pyrethroid component may flare-up aphids. If a field needs to be treated for both aphids and bollworms, Prevathon can be tank-mixed with any of the commonly used aphidicides such as acetamiprid (Intruder).

Along with the proper insecticide selection, coverage is also important getting the desired level of worm control. In fields with dense plant canopy, it is important to get material down in the lower canopy where worms are in protected places.  Air induction nozzles recommended for newer herbicide technologies produce coarser spray which may not penetrate through the dense plant canopy and provide thorough coverage. Penetration through plant canopy can be improved with flat fans or hollow cone tips and by increasing final volume (no less than 10 GPA with a preference of 15 GPA for ground rig). If using an airplane, use at least 5 GPA. 

Tuesday, July 25, 2017

Sorghum Headworms Abundant

Sugarcane aphid is just beginning to build in fields in select counties on the Southern High Plains, and as of this writing I know of no fields that have required treatment. The sugarcane aphid distribution map can be found here. So far the aphids are building fairly slowly.

The less than good news is that fairly high numbers of headworms (corn earworm + fall armyworm) are being found in panicles. I was in a field in northeastern Crosby county last week that had 1-3 medium to large worms per head, and this field was later treated. Katelyn Kesheimer, IPM Agent in Lubbock and Crosby counties, just reported a field near Shallowater in Lubbock County that had a large number of worms. Stan Carroll, the Research Technician who runs the cotton bollworm/corn earworm traps at the Lubbock Center, told me this morning that he emptied the traps Tuesday night and had a high number of moths in them when he checked them Wednesday morning. We are therefore experiencing a big flight of cotton bollworms/corn earworms. The good news, if you can call it that, is that the fall armyworm trap captures are still well below average.

Insecticide selection for headworms is complicated now that we have sugarcane aphid or the threat of sugarcane aphid in the system. Most of our older insecticides like pyrethroids, Sevin, Lannate etc. will provide control, but they will also eliminate the beneficial insects from the field and leave it more open to damage by the sugarcane aphid. Newer insecticides like Blackhawk and Prevathon will preserve the beneficial insects, but they are more expensive than the older products. Besiege is a combination product, it has the same active ingredient as Prevathon but with pyrethroid as well. Besiege will not preserve beneficial insects. If a headworm treatment is needed then the risk of sugarcane aphid will have to be factored into the choice of insecticides. As an additional complication, we think our corn earworm is still susceptible to pyrethroids in spite of some slippage downstate, but we know that fall armyworm is less susceptible to pyrethroids, especially the larger worms. One good thing is that headworms do not require the high gallons per acre of spray that sugarcane aphids do, so applications can be made with 3-5 GPA - but check the label for the specific product you intend to use.

Treatment thresholds are based on the size of the worms, number of worms per acre, heads per acre, control cost and value of the crop. For example, in the table below a treatment would be justified at 14,000 large worms (longer than 1/2 inch) per acre when the cost of control was $10/acre and the grain value was $7.00/cwt. To put this in perspective, if the field had 28,000 plants per acre, this would be one large worm per two plants. The online headworm calculator is here.


Wednesday, July 19, 2017

Texas High Plains Cotton: Stay Vigilant for Bollworms

Suhas Vyavhare, Extension Cotton Entomologist, Texas A&M AgriLife Extension Service


We have a wide range of cotton out in the field. Early planted fields are in bloom while some of the late or replanted cotton is a little behind. Overall, insect pest pressure remains light. Cotton fleahopper wouldn’t be an issue post bloom, however, the younger cotton should continue to be monitored for fleahoppers.

I haven’t come across any significant worm activity in the region yet. However, with the cotton blooming and the recent rain putting on some new extra growth, bollworm moths can be attracted to it. With so much talk going around with bollworms breaking Bt shields in south Texas and other parts of country, we need to be more vigilant. Treatable levels of headworms (bollworms) have been spotted in some of the sorghum fields around, which also warns of a potential threat in cotton.

I wouldn’t rush with insecticide application just seeing egg lay or the smaller (<1/4 inch) worms in Bt cotton; worms first need to feed on plant for the technology to show its effect. Similarly, I wouldn’t pull the trigger in non-Bt cotton based upon egg lay because natural control often helps keeping bollworm numbers in check. Give the technology (Bt traits) and the predators a chance to work their magic first.

The extent of fruit damage and the presence of live worms should be taken into account while making decisions about insecticide applications. The threshold is 6% fruit injury (post bloom) with the presence of live worms in both Bt and non-Bt crop. Some of the old data indicates pyrethroid insecticides may still work against cotton bollworms but no recent susceptibility data are available from the High Plains. The diamides (Prevathon and Besiege) are the most effective insecticides. Besiege contains both a diamide and a pyrethroid so it would be a better choice if stink bugs are present too. If stink bugs aren’t an issue, prevathon is a better option--it is always good to avoid unnecessary pyrethroid applications to keep secondary pests (aphids and spider mites) at bay. 



 

Wednesday, July 12, 2017

Grain Crops Quiet For Now

As we hit mid-season, things are relatively quiet in area grain crops. The three intense storms that passed through recently brought both blessings and challenges, but one very positive aspect is that they decimated the large fall armyworm flight that was underway. Daily trap counts dropped from 100 or so per night to almost zero immediately after the storms. Intense rain and high winds likely knocked a lot of moths to the ground where mortality factors could act, and they also washed most of the egg masses off of plants. This week's fall armyworm graph is presented below. However, for those who do not get his newsletter, Tyler Mays, IPM Agent in Gaines, Terry and Yoakum counties, last week reported fall armyworm trap captures in excess of 500 and 600.

Sugarcane aphid is still hard to find in area sorghum, and once again relatively early planting seems to have paid dividends. Most early planted fields are now in bloom, and if the aphid comes it will be relatively late in the development of the crop. Dr. Katelyn Kesheimer, IPM Agent in Lubbock and Crosby counties, has been scouting sorghum intensely since the fields dried up enough to permit it. She reported that the only sugarcane aphids found to date are in low numbers in the same forage sorghum field near Lubbock where they were found several weeks ago. There are a few yellow sugarcane aphids and greenbugs.

Spider mites are present in area corn and should be scouted. Thus far I have not heard of any treatable populations, but mite numbers often increase dramatically as corn enters the reproductive stage.

The one source of worry is that the rains also decimated the populations of beneficial insects, and this means that if sugarcane aphids, greenbugs, yellow sugarcane aphids, spider mites or caterpillar pests begin to build up there is almost nothing left to stop them. Population increases in all of our pests could occur very rapidly. 

Thursday, June 29, 2017

Texas South Plains Cotton: Shifting Gears Towards Cotton Fleahopper

Suhas Vyavhare, Extension Cotton Entomologist, Texas A&M AgriLife Extension Service

Showers over the last week should help cotton that was struggling earlier to stay alive and catch up with the progress. Most fields should fairly be safe from thrips at this stage. Many fields have already started squaring and becoming more attractive to flower feeding plant bugs such as the cotton fleahopper. Cotton fleahoppers prefer to feed on small squares (pinhead size) and can drastically reduce the fruiting sites in no time when in large numbers. When scouting for fleahoppers one should pay attention to both number of insects in field and the percent square retention especially during the first three weeks of squaring. I haven’t seen any major cotton fleahopper activity yet as numbers still remain scarce. This may be due to earlier hot and dry spell and the unavailability of alternate host plants to buildup fleahopper populations. However, fleahopper populations are unpredictable and can rise quickly in spots which is why it is important to keep a close watch on them. If you are seeing any square loss but no signs of plant bugs—that could just be the hot and dry weather causing it.
 Here is a link to access our new fact sheet for more information on the management of cotton fleahopper.

Also, check out our video to learn more about the cotton fleahopper and how to scout for it:


Wednesday, June 28, 2017

Fall Armyworm 2x Normal and May Be On Fast Increase

After a very quiet spring, fall armyworm trap captures shot up this week to twice the 6-year average. The average trap capture this week was 228, but significantly, 106 of these were caught in the last two nights. This indicates that a possible very rapid population increase might be underway.


I was taking data this morning in a corn trial near Ralls. The corn was at V8 growth stage, and the non-Bt corn in the trial ranged from 20 - 50% of the plants per plot with fall armyworm damage. In the plots with the most damage, the average damage rating was 5 on a 1-9 scale. This is still below the level of concern, but if we are indeed in a time of rapid fall armyworm increase then noticeable damage in sorghum and non-Bt corn will be appearing soon.

Wednesday, June 21, 2017

Fall Armyworm Numbers Rebuilding, Sugarcane Aphid Moves Closer

After what has been a wonderfully quiet spring, the first day of summer brings news that fall armyworm numbers are on the increase. The trap captures at Lubbock jumped in the last week and are now near the 6-year average. Expect to start seeing damage on whorl stage corn and sorghum.


Additionally, sugarcane aphid has been confirmed in Tom Green and Nolan counties. This is discussed on the Sugarcane Aphid News site here.