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Efficacy trials of OMRI approved materials on vegetable crops

Potato leafhopper

Surround is a formulation of finely ground kaolin clay that has been reported to reduce insect feeding in many crops. Potato leafhopper (PLH) is a serious pest that is very difficult to manage in organic management systems. Toxins injected into the plant when the insects feed cause leaflet curling and leaf edge browning accompanied by potentially significant yield reduction. Two rates of the commercial formulation of Surround and two experimental formulations were included a 2001 potato leafhopper trial. The trial was planted with the variety Superior. It was a good year for a leafhopper trial; leafhopper numbers were relatively high and there were good differences between treatments. Treatments were applied five times at approximately weekly intervals starting June 26th. Hopperburn was rated on a 1-4 scale as follows:

  1. Little or no leaf curling

  2. Moderate leaf curling plus some leaflet necrosis

  3. Severe leaf curling accompanied by leaf necrosis

  4. Most lower leaves necrotic and/or dead

Mean PLH Mean Hopperburn

Treatment nymph/5 lvs* Rating Yield (cwt/A)

Surround WP (13.5 lb./A)

11.8 3.2

142.0

Engelhard KV-36 (13.5 lb./A)

12.2

3.5

173.8

Engelhard KV-3 (13.5 lb./A)

12.8

3.5

184.0

Surround WP (20.5 lb./A)

13.8

3.3

155.2

Untreated control (water)

16.5

3.6

140.2

* Seasonal mean

I can’t assign letters indicating significantly different means to this table without breaking statistical rules because the validity of the test that was used to see if the means are statistically different depends on all of the treatments (there were 28). In the context of the larger trial, all the kaolin formulations reduced the mean number of leafhopper nymphs compared with the untreated control. The two Surround treatments reduced the mean hopperburn rating compared with the control, but the rating reductions did not translate into significant increases in yield compared with the control. The reductions in leafhopper numbers and hopperburn ratings were not enough to prevent significant yield reduction. The yields of the most effective treatments in this trial ranged from 277-305 cwt/A. Surround can be a problem in the sprayer if you don’t follow the mixing instructions on the label. Soft lumps of unwetted product can cause clogging. John Mosko from Engelhard Corporation offers the following tips for avoiding problems: