Texas LRGV Cotton: Heavy Whiteflies, Late Season Thrips

Silverleaf whiteflies infesting cotton leaf. Photo: Ron Smith, Auburn University

General Situation/ Harvest Time

Weather continues to be incredibly hot in the Lower Rio Grande Valley. Many growers were either applying the first or second round of defoliant this week to cotton while others are waiting to see what the weather will do this weekend.

Along the river many cotton fields were drying up from their last irrigation. I saw several cotton fields being harvested this week in the mid Valley area and growers also beginning to shred cotton stalks and till them under after harvest.

Every year cotton growers in the Lower Rio Grande Valley always work hard to harvest their cotton and destroy all cotton stalks by the September 1st deadline.

Cotton

Saw many cotton fields this week along the river in the Progresso through La Feria areas that have very high whitefly pressure along with high late season thrip pressure. Its important to keep cotton fields clean of whitefly pressure especially with open bolls to avoid stained cotton lint from the sooty mold that can grow on the honey dew excreted while they are feeding.

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In the same areas I was picking up on heavy late season thrips pressure that is causing the bronzing discoloration on the tops and undersides of the cotton leaves that can easily be detected on the upper portion of the cotton plant. Many fields along the river are still a way off from defoliation and so insecticide treatment might be needed if pest populations are beyond threshold.

Other cotton fields in the mid Valley and dryland areas were showing hardly any pest activity but did pick up on some light whitefly pressure in the Hargill and Monte alto areas on late season cotton.

Sesame

Was able to inspect several sesame fields this week. We have a wide range in sesame growth stages across the Valley as many fields are already drying down getting ready for harvest and then we have several sesame fields that recently just came up, as well as other fields still blooming or close to cut out.

For the last month in sesame we have been reporting sesame leafroller (SLR) feeding and damage. We have seen several generations and continue to see more as we are finding SLR adults (flying moths) in young sesame easily and many larvae feeding on the blooms and pods as well.

Please continue to check sesame for SLR pressure, especially those who have very late season sesame still in the early growth stages of seedling to early bloom were pod development is critical for maximum yield to be obtained.

I noticed several fields with high mirid plantbug (Nesidiocoris tenuis) pressure this week in sesame across the Valley. Sesame in the early growth stages of seedling to early bloom need to be monitored for mirid pressure.

Generally every year we have gotten high mirid pressure in mid to late July since 2015 and it usually hasn’t been a problem since in years past most sesame is in dry down stages going towards harvest that late season damage from mirids usually doesn’t affect yields because pods are already established.

However, this year we have had many late season sesame fields planted and are seeing high mirids infesting the sesame. While no threshold has been established for N.tenuis we did notice back in July of 2015 that it took as little as 3 to 5 mirids per sesame terminal/plant to cause significant damage.

Mirids are a type of plantbug that suck plant juices and can cause necrotic damage and stunting of growth to the sesame plant as well as injury to the pods. N. tenuis mirids adults and nymphs are lime green in color measuring no more than 5mm in size (so fairly small).

Mirid adults when their wings are closed make a heart shape that upon close observation is easy to spot. Necrotic damage will look like a reddish/brown scaring to the plant tissue along the stem, leaves and on the seed pods. Mirids N. tenuis also can be predators to whiteflies feeding on both adults and immatures in the lower canopies of the sesame when present.

However, mirids can develop successfully on the sesame plant alone and will feed on the plant more when they have depleted their food source (in this case whiteflies) or there is an abundance in mirid populations.

Signs of high mirid pressure feeding on the plants will be yellowing on the leaves and brownish necrotic damage and the curling under of the leaves. You will want to monitor for mirids and treat if necessary, since their feeding can hurt yield potential.

Products labeled on sesame that control mirids are Transform and Mustang Maxx.

You can click here to view this SLR video.




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