South Carolina Cotton: First, Let’s Talk About Aphids

Aphids on cotton leaf.

I am certainly getting plenty of calls about aphids, spider mites and plant bugs. Most folks are not seeing plant bugs at threshold levels but many are asking about aphids and what we should do.

Below are our recommendations for managing aphids in cotton. Pay particular attention to the language about natural control agents (predators, parasitoids, and a fungus). Those can provide good control of populations that seem like they are about to get out of hand.

In the past, I have seen many sprays made for aphids and then the fungus takes them out just as effectively a few days later in an adjacent field. So, have multiple stressors on the crop before you pull that trigger.

Also be aware that we have some aphid populations that are tolerant to the neonics.

Aphids Treatment Pointers

  • Treat only when high numbers of aphids are severely infesting plants, those populations are building and the margins of terminal leaves are drooping.
  • Aphids will cause more damage when plants are suffering from lack of moisture, and there are few signs of natural control agents.
  • If there is evidence of widespread parasitism (dead aphids, tan colored and swollen in appearance) and/or fungal pathogens (diseased aphid bodies have a grayish-green colored fuzzy appearance) an insecticide should not be applied.
  • Avoid unnecessary insecticide applications, as subsequent reductions in beneficial populations can result in damage from bollworm and fall armyworm.

Neonic Tolerance Isn’t Something New

It looked like we had some tolerance to some neonic active ingredients several years ago. Acetamiprid (Assail) has always been a good material, as has flonicomid (Carbine), dicrotophos (Bidrin), and sulfoxaflor (Transform).

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Please note, though, that Transform is not labeled for use on cotton without a Section 18 (emergency use). We applied for that Section 18 for tarnished plant bugs but have not heard back yet, so Transform use in cotton is not legal in South CarolinaC in 2019.

If I had to spray for aphids, I would probably use acetamiprid (Assail) or flonicomid (Carbine), but please note that these materials are relatively weak on tarnished plant bug. So, any attempt to control aphids and plant bugs with the same material might disappoint.

Dicrotophos (Bidrin) is usually good on aphids, but you don’t want to spray Bidrin this early, as it will likely result in a significant premature disruption of beneficials just before we get a flight of bollworm out of corn. Save that material for control of stink bugs later.

Cotton Blue Disease – Yet Another Factor

As you maybe have read or heard, cotton aphids are capable of transmitting a virus (cotton leaf roll dwarf virus – CLRDV) to cotton that can result in a disease called cotton blue disease. I dislike that name, but it apparently gets that name from one of the symptoms where the leaves are darkened to a bluish color.

The other symptoms are tightly stacked nodes, cupped and crinkled leaves, and other discolorations. We will be looking closely at the disease this season and researching many aspects of cotton aphid as a vector. Despite the news of this virus and potential yield loss, we should not spray every cotton field with scattered pockets of aphids.

Copious amounts of data clearly show that aphid sprays typically don’t pay for themselves. That said, carefully watch aphids and work with your county agent and consultant – and call me also, if you want – on aphid treatment decisionss.

In certain instances, treatments are warranted, and those are usually very bad situations with too much stress on the plant. Next week might add too much stress in places with the heat and lack of rain in the forecast, so let’s do this field by field, and get it right.

Other Pests Waiting In The Wings

Spider mites are probably going to get bad again soon, considering that rain chances seems to declining with every forecast. So, look for stippling on the upper surface of leaves around the venation and also for pale areas underneath the leaves between the leaf venation where mites and eggs will be.

So far, tarnished plant bug (TPB) populations around the state have varied. That pest is truly one that must be scouted for and managed field by field. If you spray the entire farm because one field was close to threshold, you are likely wasting money on many of the acres.

Very few of the fields my crew and I have surveyed have had populations at threshold (8 TPB/100 sweeps). So far, most issues with square retention have been related to the weather.


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