Beating Trees to Beat Bugs

SUMMARY: To decide what insecticides to apply in the spring, it is important to scout in April to determine if twig aphids and mites are present in a field. Use foliage beats for twig aphids and examine shoots for rust mites and spider mites. Always use a hand lens. Though scouting takes time, it will end up saving both time and money by helping to determine exactly what pesticides, if any, are required.


I finally made it to Ashe County yesterday. It was good to at least make it into Christmas tree country again. I saw several blue birds which is always fun.

Bryan Davis and I chatted with some growers who had treated different blocks of trees with Dimethoate + Asana at different times -- anywhere from the end of June through mid September. They wanted to know if they had controlled the elongate hemlock scale and if they could skip twig aphid treatments in the spring. It will provide us a great opportunity to evaluate different timing of these materials for both scale and twig aphid control. After all, most of the fall treatments that have been followed over the last several years have been with Talstar, not Asana. It will be interesting to see under different conditions how well the Asana performed. But our conversation also made me realize what all growers will be facing this spring.

Of course it's so snowy, you can't even get out in the field now, even if you could tell anything about pest control. If you can make it to the field, there is a layer of ice on the snow that makes walking difficult. People are sitting around knowing they are already getting behind this growing season before it even gets started. In the spring, growers need to plant, fertilize, get herbicides out and insecticides. Some even have a bit of shearing that needs finishing. I'm afraid, scouting may be one of those things that doesn't end up getting done.

How do you get it all done when you don't have the time? Fortunately, scouting doesn't have to take a lot of time. The two most important pests a grower needs to evaluate in the spring are twig aphids and rust mites. Neither should take a lot of time to assess. As pictured with this post, taking beats of foliage on just a few random trees in each block will let you know if fall treatments with insecticides have controlled twig aphids. Start this in mid-April.

This photo shows a beat with a lady beetle larvae (the big bug) and four twig aphids (one fairly big and three small). Always use a hand lens when you look at what fell out. If you find more than a couple of trees with twig aphids, you will need to treat again in the spring. At the same time when you look for twig aphids, pull a few shoots and look with a handlens for rust mites. If there are only a few, make a mental note to check again in a few weeks to see if the numbers are increasing. Remember that rust mites are very small. If you are just looking at foliage beats, you'll miss finding all but the heaviest populations of rust mites. By taking both foliage beats and pulling shoots, you will also learn if spider mites are a problem.

The fields I mentioned earlier that had had Asana in the summer or fall are much more likely to have rust mites this spring -- but there's no reason to assume mites will cause enough damage to worry about. The earlier the Asana was applied, the more of a problem rust mites are likely to be, so we advised the growers to scout those fields first. But if this spring stays fairly cold and wet, rust mites might never become a problem. As I start getting out in the field in March, I'll let everyone know in this blog what this spring looks like as far as rust mite pressure in general.

Unfortunately, some growers seem to be skipping scouting, and just treating everything in the spring with Dimethoate + Thionex, thinking that these two materials will control everything. After all, Dimethoate will control spider mites, rust mites, twig aphids and some scale, and Thionex will control twig aphids and woollies, and neither is that expensive. But remember, Dimethoate's control of mites can be short lived, and Thionex gives no added help with scale control. Twig aphid control with Thionex has been variable, and we're not sure why. These are also the two most toxic insecticides that growers use, and they also smell really foul, making them an issue with neighbors. And why spray anything at all if you don't need to? If you treated last summer and fall, you might not need to treat again this spring. And even if you didn't, twig aphids and mites aren't always a problem every spring.

Scouting takes time, but it also saves time, money and pesticides. If you aren't confident about scouting, call Extension for help. There are also scouts working in the counties that can be hired to do your scouting for you. For their names, call the County Extension Agents in some of the bigger tree counties.

I hope to get out to the fields we talked about yesterday and some I treated last fall starting the second week in March. I'll let you know what I find. In my next post, I'll go over some of the pesticides and timing that can be used for pest control this spring. But remember in April, to take your beat sheets (white plastic plates work great --thanks for that tip Doug Hundley!) and hand lens with you.