Black aphids can be one of the most difficult pecan pests to manage because they often slip in, do their damage, and are gone before you know they are there. For this reason, they require pretty intensive scouting on susceptible varieties like Schley, Sumner, Oconee, and Gloria Grande. Anyone growing these varieties probably needs to check for black aphids at least twice a week from July through August. There is normally a flight of black aphids that comes through sometime in early June. These are usually winged adults that come through to feed, damage a few leaves and condition the foliage for the later generations (black aphids reproduce more and develop more rapidly on damaged foliage).
The late season generations, which we see during this time of year, can develop into a problem very quickly, causing the characteristic yellow spotting, developing necrosis, and eventual loss of leaves. Tolerance for black aphids at this time of year should be very low because August is a critical month for both the current season’s crop and the crop potential for next year. Thus, trees should be kept as stress free as possible at this time. For this reason, it is recommended that pecan trees are sprayed when only 15% of the terminals sampled have more than one black aphid adult with nymphs present on a compound leaf.
Black Aphid Adult Black Aphid Nymphs
We have several good materials labeled for black aphids. The recently released products Closer and Beleaf have given excellent control with good residual. Fulfill also works well if applied before populations get too heavy. If mites are found in the orchard at the same time as aphids, Nexter is a good choice. Another less expensive alternative is the highest labeled rate of imidacloprid. I have seen this work well in some orchards and less so in others. Those cases of poor results with foliar-applied imidacloprid may be related to high pH of the water in the tank, which can break down imidacloprid, or to UV light exposure when spraying in the middle of the day. At any rate, some may choose to include Chlorpyrifos along with the imidacloprid to get a quick knockdown of black aphids. If you choose to spray Chlorpyrifos, be aware that you may see a rebound of aphids and mites in the coming weeks.
ProGibb applied at 10 oz/acre earlier in the season before damage is visible can mask the symptoms of yellowing that occur from black aphid feeding. This prevents the development of high populations in later generations since they do not reproduce as well on undamaged foliage. It is probably too late in the season at this point to get the benefit from ProGibb if you already have black aphid damage present but if ProGibb is applied be sure and use the 4% material. There is another formulation that has a higher ai, which can affect the return crop.