Important: Postively I.D. the Insects on Your Farm

This week in my Transitioning/Beginning Organic Production class we talked about insects. We had 2 great presenters. First up was Diane Almond from Honey Bees and Heather Farm in Fletcher. Diane discussed pollinators and the importance of maintaining pollinator habitats on your farm or garden. Diane's talk had me on the edge of my seat!

Second up was Amanda Stone, agriculture agent in Buncombe County who works with the Green Industry. Amanda's presentation included, not only a peek into her insect collection, but insect management techniques in organic systems, which includes increasing biodiversity, employing cultural methods and mechanical means and finally the use of OMRI-approved materials. One aspect of Amanda's discussion was the importance of scouting. Scouting for insects, mites and disease problems is the foundation for Integrated Pest Management or IPM. Scouting for insects on your farm lets you know what is on your crops, when they arrive, how many are present and if there has been changes in severity of infestation, and will help you to decide whether or not to take action.

Interestingly, this week a grower sent me some pictures of a "worm" he found in his Napa Cabbage. Because I had never seen this before, we sent the images to the NCSU Plant Disease and Insect Clinic. We got results just a day or so later!

Syrphid fly maggot (larva) found on Napa Cabbage. Photo courtesy of Michael Porterfield.

Syrphid fly maggot (larva) found on Napa Cabbage. Photo courtesy of Michael Porterfield.

The entomologist at NCSU informed us that it was the larva of a syrphid fly (some call these hover flies or flower flies - check our Debbie Roos photo an adult and some other incredible photos of syrphid flies and larvae).

The syrphid fly is actually a good guy, a beneficial insect, in the farm or garden! When syphids are present, you can just about guarantee there are aphids present as well. Syrphid larvae can do a remarkable job of cleaning up low aphid populations. Each larva can consume up to 400 aphids during their development!

Syrphid fly larvae do not cause damage to the plant. Syrphid fly larvae may cause a problem if they are present on your crops at the time of sale. At the point of sale, essentially all insects are considered "insect contamination". For folks selling directly to consumers, education may be the key to overcoming this notion. For growers who are not selling directly, know the level of contamination that your market will tolerate.

It was a great thing that the grower was scouting his fields! As a result, the grower was able to positively identify the larvae and decide whether or not to take action. We also learned more about biocontrol on the farm and syrphid fly and aphid relationships.

Please take the time to scout your fields as often as possible, you will learn a lot about your crops!

**Special thanks to Dr. Mark Abney for doing a bang up job identifying the syrphid fly and to Michael Porterfield for taking these great images!**

Downy Mildew: Cabbage

Today I went to a field of cabbage, a nice change from all of the time I have been spending in tomato and pepper fields. I noticed that the lower leaves had some spots that were yellow and turning necrotic. When I turned the leaf over I notice that familiar fungal growth- downy mildew.

Symptoms of downy mildew on cabbage include irregular shaped lesions that vary in size and are sunken and whitish-gray (image, left). The tissue around the lesions will turn yellow. When you flip the leaf over, a fluffy, white, downy growth is evident (image, below). One can distinguish downy mildew from powdery mildew because only downy mildew will sporulate (reproduce new spores) on the bottom side of the leaf.

Downy mildew on cabbage is caused by Peronospora parasitica. This organism causes downy mildew on vegetables in the Brassicacea family such as broccoli, cauliflower and radishes, and is different from the organism that causes downy mildew on cucurbits (Pseudoperonospora cubensis). P. parasitica, like most downy mildews, thrives in cool, wet weather (temps. 50-60 degrees F) though it can tolerate cooler and warmer temperatures.

P. parasitica forms two types of spores, oospores and sporangia. Oospores are the overwintering, resistant spores that can survive in the soil (not shown). The other spore type are sporangia. Sporangia are large (relatively speaking for a microscopic organism), round spores that are born on tree-looking structures known as sporangiophores (images left and right). These sporangia are disseminated by wind or rain splash. Isn't this organism beautiful (I know, I know... a face only a plant pathologist could love). Making a successful slide is difficult because P. parasitica is quite delicate. You will notice that some areas of the image to the left are out of focus, this is because P. parasitica is 3-D and taking a 1-D image doesn't do it justice.

Downy mildew can be introduced into a field through transplants, so make sure that your transplants are disease free. Also, if you notice that you have diseased plants, do not dump these plants in a cull pile in the field because they have the potential of infecting the non-diseased plants. Try to eliminate brassica weeds and rotating the field with non-brassica vegetables might help.

There are no downy mildew resistant cabbage cultivars, however there are a few effective fungicides for the control of downy mildew on cabbage. A new fungicide from Syngenta, Revus (mandipropamid) has shown excellent efficacy for controlling this disease. Also, ProPhyt (potassium phosphite) + Manex (maneb) can be used to control the disease.
Reduced efficacy of Ridomil Gold and Bravo has been shown in NC (Adams et al., 2007, Plant Disease Management Reports 2:V119. DOI:10.1094/PDMR02).

As always refer to manufacturers' recommendations on the fungicide label.

**Special thanks to Kelly Ivors and Dreams Milks who assisted with the pictures of P. parasitica.**
*Much of this information was gathered from Univ. of FL Plant Pathology Fact Sheet 33 (Tom Kucharek) available on-line.*