Thursday, July 14, 2016

Southern Plains of Texas: Time to Look for Lygus

Suhas Vyavhare, Texas A&M AgriLife Extension Service

With the daytime highs over 100 degrees almost each day, cotton is squaring with some fields starting to bloom. Although we have received light and spotty showers, we need more over the next couple of weeks for the cotton to continue to grow. Insect pressure remains very low in most places. I know only of a couple of fields that needed to be treated for cotton fleahoppers (Swisher County) so far. Cotton fleahoppers are generally considered a pest in early squaring cotton. As plants increase in size and fruit load, larger numbers of fleahoppers may be tolerated without yield reduction.

With the fields starting to bloom, the next insect pest we
should look for is a lygus bug. Both adult and immature lygus can feed on cotton with their piercing and sucking mouth parts. The damage occurs primarily by insect feeding on the squares and small bolls.  As a result of lygus feeding, small to medium sized squares usually darken, shrivel and fall from the plant, while larger squares may remain on the plant. Flowers that develop from squares damaged by lygus may have tan to brownish colored markings and are referred to as dirty blooms.
Lygus feeding on bolls causes small black sunken spots on the outside of the boll.  Small bolls are most susceptible to lygus damage, while bolls that are larger than 1 inch in diameter are generally safe from lygus damage. Bolls that are 1/2 inch in diameter or smaller will often shed due to heavy lygus feeding.  

Alfalfa is a significant source of lygus, and large populations of lygus may disperse into nearby cotton when the alfalfa is cut.  Significant dispersal can often be eliminated by strip or rotational cutting of areas of the alfalfa.  Lygus prefer alfalfa over cotton and if suitable alfalfa is available, lygus will primarily move into the uncut alfalfa rather than the cotton.  Similar tactics can be used for weedy areas.  Avoid mowing or plowing weedy areas infested with lygus, or leave portions for lygus to disperse into rather than the cotton.

We are seeing a good numbers of big-eyed bugs, damsel bugs and collops beetles in cotton that are notable predators of lygus eggs and small nymphs.  Spiders prey on nymphs and adults as well.  Avoiding killing these natural enemies with broad spectrum insecticides will enhance lygus management and may prevent the development of damaging populations. We have just produced a new video on scouting for Lygus in cotton. (https://www.youtube.com/watch?v=gfSM8jF_Rqs )

Lygus Action Threshold

Sampling method
Crop stage
Drop cloth
Sweep net
1st two weeks of squaring
1-2 per 6 ft-row with unacceptable square set
8 per 1oo sweeps with unacceptable square set
3rd week of squaring to 1st bloom
2 per 6 ft-row with unacceptable square set
15 per 100 sweeps with unacceptable square set
After peak bloom
4 per 6 ft-row with unacceptable fruit set
15-20 per 100 sweeps with unacceptable fruit set

Wednesday, July 13, 2016

Sugarcane Aphid Management on the High Plains

Now that sugarcane aphid has been found in Floyd County it is safe to assume that we will shortly find it in surrounding High Plains counties. We all went through the aphid invasion last year and there is no need to go in to great depth on scouting and management, so I will just hit the highlights from lessons learned last year. If you want to read our complete 2016 sugarcane aphid management publication it is here.

Early planting is going to pay off

The earlier the aphid arrives during crop development, the more damage it can do. Infestations prior to boot can cause sterile panicles and decrease yields to essentially zero. Infestations at or after flowering, while still very serious, are somewhat less potentially damaging. This is why our treatment thresholds vary by crop stage.

Treatment threshold:
Pre-boot: 20% of plants with aphids.
Boot: 20% of plants infested with 50 aphids per leaf.
Flowering to Milk: 30% of plants infested with 50 aphids per leaf.
Soft dough through dough: 30% of plants infested, localized areas with heavy honeydew, and established aphid colonies.
Black layer: Heavy honeydew and established aphid colonies with treatment only for preventing harvest problems.

Our earlier planted sorghum has either finished flowering or is now flowering and has moved to the place it can withstand more aphids. In part this might matter because we have a relatively high number of beneficial insects in the system, and they have a better chance of keeping populations below treatment thresholds when those thresholds are higher. And even if one insecticide application is necessary, the need for a second application is far less likely in a much more mature crop.

Weekly scouting is a must

Under hot, dry conditions, the reproductive capacity of this aphid (which is born pregnant) is something approaching Shock And Awe, and everyone who went through the 2015 season will agree.  Missing a weekly scouting might mean missing populations low enough to be brought under control with insecticides. In 2015 we had many fields that were sprayed too late and adequate control was not achieved without a second application. Once the aphid has been found in a field, then twice-weekly scouting is important. Last year I would have linked to our guide to recognizing the sugarcane aphid, but this year I think we all know what the enemy looks like.

"Tolerant" hybrids are susceptible hybrids

There are a few hybrids with resistance to sugarcane aphids, although the seed industry chooses to call these "tolerant" hybrids because they rightly don't want to give the impression they are bulletproof. Our best resistant hybrids are what could be called moderately resistant, and this won't stop the aphids from reaching treatment thresholds. It may slow them down, and it may let the beneficial insects have more time to exert control, but all other things being equal it is merely a delaying action. Fields of "tolerant" hybrids should be scouted and sprayed based on the treatment threshold just like fields of completely susceptible hybrids.

Insecticide choice matters - a lot

Last year saw everything in the book, and some things not in the book, being thrown at sugarcane aphids. Many of these insecticide products were our old aphid standards, and what we found was that they were not very good at killing aphids, but they were very good at killing beneficial insects (the big guns in aphid control after an application). Our insecticide trials confirmed this; we had massive aphid resurgence where we killed the beneficial insects. There are only two good insecticide choices for sugarcane aphid: Sivanto and Transform. Both of these provide high efficacy with minimal impact on beneficial insects.

Make the first application count

Last year we observed insecticide applications of Sivanto and Transform made with high rates and plenty of carrier volume most often did such a good job of control that the few surviving aphids were cleaned up by beneficial insects. Conversely, we observed that fields sprayed with lower rates and/or insufficient carrier volumes frequently did not get control and required a second application.

Experience is a good teacher

This pest is manageable. Last year was a bit of trial and error, but after one growing season of intense aphid pressure we are much better equipped in 2016.

Friday, July 1, 2016

Southern Plains of Texas: Time to Look for Fleahoppers

Suhas Vyavhare and Blayne Reed, Texas A&M AgriLife Extension Service

The high temperatures, high humidity, and the passing of light cotton showers over the last couple of weeks have been very conducive for rapid crop growth and development. Most cotton fields on the Southern High Plains are past the 5th true leaf stage and are sporting pinhead through ¼ grown squares.  This should mean they are no longer vulnerable to economic damage by thrips. There are some late fields and re-planted fields which can still be injured by thrips, however, and we should continue to scout these fields for thrips. With the high temperatures potential for rapid plant growth, and a lessening thrips pressure in general these field might be able to escape from any serious thrips damage.

As the crop is approaching reproductive phase, we should be looking for fleahoppers—many of us scouting regularly in the field are already seeing a few on squaring cotton.  There are already a small handful of regional fields reaching an economic level for this pest.  If you see the smaller and freshly adorned squares turning brown and dropping to the ground, and / or missing from the plant, the problem could be physiological or weather related but most likely the damage was caused by fleahoppers. Fleahoppers can be found in abundance on their preferred weedy hosts like silver leaf nightshade, woolly croton and horsemint. Although cotton is not the primary preferred host, it is a choice secondary host that fleahoppers will move to once weeds are killed by herbicide application, mechanical cultivation, or physical hoeing .

The adult fleahopper is about 1/8 inch long, pale green, and have piercing and sucking mouthparts which they use to suck proteins and other nutrients from the developing squares. Their bodies are flat with an elongated, oval outline and prominent antennae. As their name suggests, they do slightly resemble a whitish or yellowish-green flea, mostly due to the appearance of their hind legs looking much like the hind legs of a common cat flea.  Nymphs resemble adults but lack wings and are initially almost white in color or sometimes pinkish until they feed. After feeding, the immature stage is pale green with prominent, often reddish eyes.

Both adults and nymphs suck sap from the tender portion of the plant, often targeting the smaller squares (immature flower buds).  Matchhead, pinhead, and even smaller size squares are the preferred cotton feeding sites even after the plant develops larger squares.  Unfortunately the all-important first squares put on the plant are at the most risk.  While cotton has the ability to replace some level of early fruit loss, losing too much early fruit set will affect cotton’s growth patterns causing rankness and could impact fiber quality by the end of the season via fruit maturity. When fleahoppers are abundant, heavy early fruit loss may occur. Cotton is particularly susceptible to cotton fleahopper damage during the first three weeks of squaring but remains at risk until the second week of blooming when blooms become widely abundant throughout the field.  At that time, fleahoppers will feed upon readily and easier accessible pollen and be of no economic importance.  Later in the season, fleahoppers are known to even feed upon a few bollworm eggs and small larva as a predator, but early season economic populations should not be ‘saved’ for any beneficial potential. 

The 1st week of squaring economic threshold for fleahoppers in match head stage cotton is 35% infested plants with 90% square set or worse.  This percent fleahopper infested plant calculation can be made via whole plant inspection or beat bucket methods.  As plants get older, many entomologists prefer to scout for fleahoppers with drop cloths or sweep nets.  This allows the field scout to check dozens and hundreds more plants over the same period of time scouting in the field.  The 35% infested economic threshold and treatment level translates into roughly 1 fleahopper / 1.5 – 2.5 row feet for the drop cloth or sweep net method with the same percent square set calculation. 

As cotton plants develop, higher levels of fruit loss to fleahoppers becomes acceptable.  Given sufficient time and if early losses were not heavy enough to impact plant development, cotton is often able to compensate for lost squares during the pre-bloom period with little impact on yield, up to a point.  Thankfully, quite a bit of research has gone into finding those levels.

Cotton fleahopper action threshold is 25-30 cotton fleahoppers/ 100 terminals with:
Week of squaring
Square set
1st week
<90 percent
2nd week
<85 percent
3rd week to 1st bloom
<75 percent
After 1st bloom
Treatment is rarely justified