Spotted Wing Drosophila (SWD) as of Oct. 3, 2012 and Your Winter Plans
Posted: October 3, 2012
1) As of now, SWD seems to be just about everywhere. In earlier articles, I had mentioned that we were finding SWD in fruit crops long after harvest was complete. In one cherry orchard that we are monitoring, SWD has been caught in traps every single week since early July - even though had been no cherries at all on these trees due to spring frosts. In fact, numbers are actually growing up there now. Most puzzling… Then folks from the Pa. Dept. of Agriculture reported that they were finding SWD in lumberyards far from any commercial fruit production. All of this tells me that SWD is likely hanging out wherever they are protected, perhaps under tree bark or in tree cervices. It also makes me wonder whether they can use sugary sap as a food source, perhaps taking advantage of holes in trees made by other pests. I don’t know, and I’m just wondering… but it’s something we should figure out so we can better understand this pest.
2) SWD is very fond of wild fruit hosts that we have in PA. The highest number that I’ve caught so far this year on a per-day basis (as of two days ago, over 100 SWD in a little over 24 hours in one vinegar trap) was in pokeweed. Extension educators have been monitoring crops in different locations, and where traps are both in commercial crops and wild hosts such as blackberries, the higher trap catches have been in the wild hosts. This is likely because the wild hosts provide SWD with un-harvested fruit in which to multiply. Wild hosts are also usually in wooded areas with dense foliage that provides high humidity and moderate temperatures. Put all of these conditions together, and you have an environment in which SWD thrives.
3) Neighboring crops seem to make a difference. If a preferred food source is present (so far, nearby cherries and cantaloupes/muskmelons that split seem to be problematic), later fruit crops are at high risk. However, it looks like the reverse may also be true. On our research farm, the fall-bearing raspberry and day-neutral strawberry plantings are each surrounded by non-SWD hosts - grain crops, buckwheat, and grass. So far we’ve had relatively low SWD populations in the raspberries, and no SWD in the day-neutral strawberries (but that does not mean that you should rest easy if you have a similar situation). While neighboring plants can be problematic, it makes me wonder whether some might have potential as a trap crop if a buffer area is used.
4) Growers who have had the best success with keeping SWD at bay have been aware that SWD was present early and kept after them to keep populations low (and hence multiplication potential low as well). In situations where SWD populations got a head start, the growers had problems with getting the situation under control or just gave up on harvesting the crop.
5) Research is progressing. Right now we’re doing a lot of work with different baits for monitoring. Other researchers are making progress in other areas, so by next spring we’ll have some improved recommendations. By the way - at the next Mid-Atlantic Fruit and Vegetable Convention in Hershey (Jan. 29-31, 2013) there will be a large cross-commodity session on invasive pests and weeds Thursday afternoon. This will be in place of individual sessions, since these invasives are affecting growers of both fruits and vegetables.
So, what does this have to do with your winter plans? If you have nearby wild berries, you might want to treat them with an herbicide this fall, cut them back this winter, and keep the areas mowed next spring. As you plan where you are going to plant next year’s crops, you might want to take the above information into consideration regarding farm layout. And, as always, I’d like to encourage you all to attend the Mid-Atlantic Fruit and Veg. Convention in Hershey for a nice mid-winter get-away. You’ll have the opportunity to learn the latest from researchers and other growers, and meet one of the largest groups of exhibitors you can find.
Kathy Demchak, Penn State Plant Science, email@example.com