I went out on Friday to evaluate twig aphid hatch in some untreated trees in Avery County (thanks Jerry Moody!). These trees had ice on them from the snow/sleet/freezing rain from Thursday, so it was a bit hard to evaluate twig aphids. However, the aphid eggs were very plump and ready to hatch and it appeared that a few of them had already, though I didn't see any live aphids. I estimated that about 16% of them had hatched already. Typically I see that many hatched by late March, so hatch is definitely late this year.
In most years, all twig aphids have hatched by April 15. I doubt that we have 100% twig aphid hatch by that time this year. So what does that mean for you in trying to scout and control twig aphids?
First of all, if you are scouting to determine if your fall insecticide applications have successfully controlled twig aphids this spring, you might want to wait until after the 15th. I doubt if you will see much this week in the way of twig aphids. Remember too that the aphid which hatches from the egg is the stem mother. They are all female and they reproduce without mating. At maturity they produce live young. So if you see one aphid on April 15 and your trees break bud on May 1st, that aphid has 2 weeks to mature and start reproducing. One aphid could easily turn into 15 during those two weeks. Therefore, be very cautious of scouting too early for twig aphids.
If you know you have to treat however, it's not too early to start. Any material used will last long enough to kill the aphids once they are hatched. At least one grower has already seen some rust mite activity so be sure to scout for rust mites and spider mite eggs before deciding what material to use. Also remember to protect honeybees. If the temperatures are above 50 degrees, they will be foraging in flowers.
If you are treating for twig aphids, it's a good idea to do so before cones are produced on the tree. Twig aphids will hide in the cones, protecting them from chemical spray. Once the cones have come out on trees, dimethoate is one of the few materials that will penetrate them to kill the aphids in the cones.
One word about dimethoate -- if you do have to send workers in to remove cones after treating with dimethoate during the 10 day re-entry interval, they have to wear long sleeved shirts and long pants, chemical resistant gloves and chemical resistant footwear. They don't have to wear masks.
I will keep monitoring twig aphid hatch as in years past and will keep you posted on how the spring is progressing. And if you see anything interesting when scouting let me know so I can pass that information on to others.