Defoliation and Stinkbugs

Howdy,

  Our pest pressure in cotton is starting to wind down some as the bolls harden. We still need to watch out for stink bugs for a little bit longer, but the bollworm pressure has dropped off.

  We are approaching harvest for cotton, and with that comes the consideration for harvest aids. Timing of harvest aid application is important, we want to strike a balance between keeping up the lint quality in older open bolls,  but also allowing younger bolls to mature. Applying to early can halt green boll maturation, but applying late can have a negative impact on lint quality of the older bolls. Most product labels recommend application between 50% to 70% open boll, but research has shown that optimal application timing can be anywhere from 42% to 81% open boll, depending on the distribution of fruit on the plant. Cutting a cross section of a boll is another way to determine maturity. Mature bolls are more difficult to cut, and contain dark seeds, not soft seeds with a jelly like inside. Nodes above cracked boll (NACB) can also be used to determine maturity. Research has shown that harvest aids applied at three NACB will not result in lint weight loss, while applications at greater than 4 NACB can result in yield loss.

  Environmental conditions can have a large impact on how well a harvest aid will work. Ideal conditions are warm, sunny, with low soil moisture, without excessive soil nitrogen, and plants that have reached maturity and are not actively producing leaves. Nozzles should provide uniform coverage with small droplets. Spray volume should be 15 GPA for ground applications and 5 GPA applied aerially. A combination of defoliants and desiccants is often used to finish cotton out. Defoliants are broken into two categories, hormonal and herbicidal. Hormonal defoliants include thiaiazuron, and herbicidal defoliants include tribufos and PPO inhibitors. Too high a rate of defoliants can cause leaves to stick to the plant rather than falling off. Boll openers can also be used, their active ingredient is usually ethephon, which is converted in the plant to etheylene. Etheylene causes fruit to ripen, so causes bolls to open more rapidly. It causes them to open, but it does not cause any increase in maturity, only an increase in opening.

  Check out Josh McGinty's publication for more info: http://agrilife.org/texasrowcrops/2015/08/03/preparing-for-the-2015-south-texas-cotton-harvest/

  Good luck harvesting, everyone. We have rain in the forecast, and I hope everyone gets their crop out in a timely fashion. Let me know if you have any questions or concerns, or find anything weird in the fields.

Sincerely,

Kate

Cotton Pest Update

Howdy,

  There have been a bunch of combines going this week! From what I have heard so far, most of the milo and corn is looking pretty good. The cotton everywhere is starting to crack bolls on the bottom.

  If your milo was planted late and is still a little ways from harvest, keep a close eye on sugarcane aphids. We haven't had a bad outbreak of them yet, but most of the crops I have looked at were early planted and missed the worst of the pest pressure. Pests in sorghum tend to be heavier the later the sorghum is.

  We are keeping an eye on stinkbugs and bollworms in cotton still. The stinkbug pressure has been fairly low so far, with only a few fields warranting treatment. If there is 20-30% boll damage with stinkbugs present, you may want to consider a treatment. Bollworm egg lay is going on again, so we are watching their numbers. In most places the predator populations are fairly high, so small bollworms and eggs have not made it too long. The threshold for bollworms is 5,000 worms/ acre with more than 5% damaged bolls and worms larger than 1/4 inch.

 Cotton aphid numbers have been rising, and it is a good idea to start watching them. Their numbers should stay low with all the predators we've seen lately. The main concern for aphids will be when bolls are open; high levels of the honeydew they produce can drip down and stain the lint.

  Below are some predatory insects I have been taking pictures of, please give me a call if you have any questions.

Parasitoid Wasp Pupa Casing
Photo: Kate Harrell

Dragonfly
Photo: Kate Harrell

Dragonfly
Photo: Kate Harrell

Damselfly
Photo: Kate Harrell

Dragonfly
Photo: Kate Harrell

Trash Collecting Lacewing Larvae
Photo: Kate Harrell

Have a good weekend, everyone!

Kate

Cotton Pest Update

Howdy,

  I know many of you are in the middle of harvesting sorghum, and that means we made it though without sugarcane aphid populations skyrocketing. That is fantastic, considering the winter we had. It never really got cold enough to kill anything. The corn is also finishing out, and a great deal of it looks pretty good, despite all the southern rust, northern leaf blight and other diseases we saw. The cotton is very near if not at cutout in most places. Most fields in Jackson and Matagorda counties are past cutout now, and the flowers are at the very top of the plant, if it's still flowering at all.

  The pests I have been seeing in cotton mostly are just bollworms. The stinkbug pressure has been pretty light, but we'll still need to keep an eye out for them for a little longer. Bollworms have started flying again, and I have seen new moths and some new eggs laid. We may have one more flush of these insects before the cotton in out of harm's way.

  The threshold for bollworms is 5,000 worms/ acre with more than 5% damaged bolls and worms larger than 1/4 inch. If you are seeing higher than about 25% of the plants with larger larvae on them, please give me a call and let me know. I have heard scattered reports of pyrethroids not working as well as expected, it may be good to keep that in mind if your fields reach treatable levels. This website has a decent chart on what insecticides work on bollworm if you do have to spray them.   

H. zea moth
Photo: Kate Harrell

H. zea eggs
Photo: Kate Harrell

Armyworm eggs
Photo: Kate Harrell

Bollworm Damage
Photo: Kate Harrell

H. zea Larvae
Photo: Kate Harrell

   We need to continue to keep an eye on stinkbugs, their populations will probably rise as grains are being harvested. There are also leaf footed bugs moving into cotton, but we can treat them the same way as stinkbugs, but err to the lower end of the threshold for them. They are aggressive feeders and tend to move in groups.

Stinkbug Eggs
Photo: Kate Harrell

Minute Pirate Bug Nymph
Photo: Kate Harrell 

Lacewing Larvae
Photo: Kate Harrell

  The beneficial populations are pretty healthy in most fields right now. I am hoping that will help with the new egg lay the bollworms have recently started. I've been bitten by two minute pirate bugs and lacewing larvae. If they're gutsy enough to bite an entomologist, they should make short work of a caterpillar. Have a safe weekend, everyone.

Kate

Cotton Pest Update

Howdy,

  This has been a busy field season so far. We have had just about every kind of pest pressure, and it doesn't seem to be letting up yet. Fortunately, Jackson and Matagorda county cotton is nearing cut-out, and the corn and sorghum is wrapping up in Wharton county. We are planning on harvesting the Wharton county sorghum trial on Tuesday. As folks are harvesting grain, many of the insects that were feeding in those fields will be moving into cotton in force. We'll be needing to keep a close eye on bollworm, armyworm, verde plant bug, and stinkbug numbers. It has dried out a little now, and aside from the spotty showers we've had, some fields are starting to dry out. Most of the grain crops are past watering, and are drying down and nearing harvest. I know many of the fields I have seen are rain fed only, but if you do have the ability and inclination to irrigate, keep in mind that once cotton reaches about 5 nodes above white flower (NAWF) it is unlikely that irrigating will have any impact on yield.

  Currently we are watching the bollworm populations pretty closely. We even have pretty heavy pressure in all of the Bt varieties. The egg lay has been pretty high, and is going to increase as the corn and sorghum finish. Eggs are usually on the top of the plant, but they can lay eggs anywhere on the plant. I have been finding eggs laid either on blooms or on bracts, both of which have lower expression of the Bt trait. There is a greater chance of survival when the caterpillar feeds on the flowers and bracts before trying to move into the bolls. The action threshold for these escaping caterpillars is 5,000 worms/ acre with more than 5% damaged bolls when checking three plants at a minimum of four locations in the field. I have been seeing damage that high, and many of you have made treatments. This website has a decent chart on what insecticides work on bollworm if you do have to spray them. The chart leaves out a few trade names, but is comprehensive with the chemical names. If you are seeing incredibly high bollworm populations (i.e. over 25-30% of plants infested), please don't hesitate to contact me. 

3-4 day old H. zea larvae (Bollworm)
Photo: Kate Harrell

5-6 day old H. zea larvae with cotton aphid
Photo: Kate Harrell

Armyworm egg mass
Photo: Kate Harrell

  Stink bugs are still a concern in cotton, and will continue to move in out of grains. The threshold for stinkbugs in cotton is 20% dropped bolls or bolls with warts on inner carpal walls or stained lint and finding stinkbugs in the field using a drop cloth. Check out the decision aids below for more info on stinkbugs.

  We need to continue to keep an eye on sugarcane aphid populations this close to harvest. The threshold is 50-125 aphids per leaf, treat within 4 days of reaching threshold. If we allow them to get out of hand at the end, the honeydew produced by these aphids along with the sooty mildew that tends to grow on it can really gunk up a combine. With the majority of our sorghum being a little earlier, hopefully we will miss the worst of their populations.

Unconventional Beneficial
Photo: Kate Harrell

Unconventional Beneficial
Photo: Kate Harrell

  I'd like to say thank you to everybody that invited me to field days this past month, and to the folks who have shared all kinds of summer produce. It was all delicious. Have a fantastic 4th of July, and stay safe, everyone!

Kate