Saturday, August 26, 2017

Sorghum: Sugarcane Aphids, Headworms and Midge

We have been closely monitoring sugarcane aphid numbers at the Lubbock Experiment Station and hoping the rain would knock them down. Unfortunately this has not happened, and our untreated plants in bloom now have 500 - 2,000 aphids per leaf and the lower half of the canopy has severe leaf damage. There are plenty of winged adults, too, and these will be flying off to infest other fields. With all of the late sorghum planting after failed cotton, there is now a very wide range of sorghum maturities out there and the younger plants are still subject to the full force of the aphid. High Plains insecticide action thresholds for each growth stage are presented on page 5 of our SCA Management Publication. There is also a statement about re-treatment thresholds.

However, we now have a 2-3-axis threat because cotton bollworm/corn earworm egg laying has really picked up and is now at a level of concern in both cotton and sorghum, and sorghum midge can still injure crops yet to complete bloom. In sorghum, cotton bollworm and fall armyworm comprise the headroom complex, and these insects feed directly on the developing kernels and can cause significant yield loss. Our treatment thresholds are based on the size of the worms, number of plants per acre, cost of control and market value of the grain, and these thresholds are presented on page 22 of Managing Insect and Mite Pests of Texas Sorghum. While cotton bollworm numbers are high, thankfully fall armyworm numbers are fairly low.

We think our High Plains bollworms are still susceptible to pyrethroid insecticides even though there has been some weakness in susceptibility in south Texas. A headworm population that is predominately cotton bollworm (but not fall armyworm) can be taken out with pyrethroids - EXCEPT that using them will eliminate most of the biological control in the field and stimulate a sugarcane aphid and/or yellow sugarcane aphid population increase. 

If a field reaches treatment threshold for either headworms or sorghum midge then insecticides should be applied to protect yield. However, if sugarcane aphids are present in the field then the choice of insecticide is important. We have some "soft" insecticides for headworms that will not remove the beneficial insects that are important for aphid control. Unfortunately, except for Blackhawk insecticide, this is not the case for sorghum midge, and any "hard" insecticide application (for either pest) should be followed up by careful monitoring of aphid populations. Insecticide options in these multi-pest situations are presented in "Insecticide Selection for Sorghum at Risk to Sugarcane Aphid Infestations".

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.