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.