MN Fruit & Vegetable IPM News - Vol. 1, No. 6

As the 2004 growing season began, the warm, dry conditions allowed many crops to be planted earlier than normal. The first planting date of our snap bean seed treatment trial was May 3rd with first emergence on May 14th. With the rapid crop emergence (11 days compared to 21 days in 2002/2003) we expected to see light seed corn maggot (SCM) infestations because of the short time period the seed was susceptible to being attacked. However, on May 19th we dug 3 sets of 5 consecutive seeds/plants from each plot to rate the seed/plants for SCM damage. Results indicate that in our untreated check and fungicide only plots seed/plant damage was as high as 55-58% with most damage occurring on the cotyledons (Table 1). Several rates of Cruiser 5FS and Lorsban 50WP were significantly lower than the checks with cotyledon damage ranging from 7-13%. Damage on the unifoliate leaves followed a similar pattern. However, stem damage for insecticide seed treatments was higher than for cotyledons. Although significantly lower than the checks, Cruiser treatments had stem damage ranging from 13-22%, while Lorsban held stem damage to just 2% of the seed/plants. We will not take stand counts for another week but visually it appears that the stem damage may lead to a stand loss.

Our second planting date of the snap bean seed treatment trial was May 18th. Shortly after planting the temperatures began to drop and we did not have first emergence until June 1st, 14 days after planting. On June 2nd, we dug 3 sets of 5 consecutive seed/plants from each plot. Results indicate that only Lorsban provided a significant reduction in damage to cotyledons compared to the checks (53% and 72%) with 18% seed/plants damaged (Table 1). Most treatments had an increase in cotyledon damage compared to the first planting date. A partial explanation may be the extra 3 days that the seed was in the soil before emergence which may have allowed SCM more time to locate and damage seed. As in the first planting date a similar pattern of treatment effects occurred for unifoliate damage compared to cotyledon damage. However, in the second planting date there were no significant differences for any treatments compared to the checks for stem damage. A possible explanation for this was the stage of SCM attacking the seed/plants. In the first planting date SCM were large late instar maggots, while the SCM found in the second planting date were smaller early instar maggots. These smaller maggots tended to feed primarily in between the cotyledons and on the unifoliate leaves that sit in between the cotyledons. If SCM had been older or had more time to feed on the seed/plants, we would expect the maggots to move from the cotyledons on to the stems. In addition, the stand establishment visually looks much more uniform compared to the first planting date.

Table 1. Snap bean seed treatment trial: percent and location of seed corn maggot damage on germinating seed, Rosemount, MN 2004

		Planting date #1 (5/3/04)			Planting date #2 (5/18/04)
Treatment	Insecticide Rate (grams AI / 100Kg seed)	% damaged cotyledons	% damaged unifoliates	% damaged stems	% damaged cotyledons	% damaged unifoliates	% damaged stems
1) Cruiser 5FS	30	13 c	10 c	22 bcd	55 ab	30 ab	18
2) Cruiser 5FS	50	10 c	3 c	13 cd	45 bc	27 abc	18
3) Cruiser 5FS	75	13 c	3 c	17 cd	32 bc	10 bc	12
4) Gaucho 480FS	62.5	35 bc	17 bc	30 abc	32 bc	17 bc	5
5) Lorsban 50WP	62	7 c	2 c	2 d	18 c	5 c	0
6) Fungicide only 1	--	58 a	42 a	47 a	53 ab	25 abc	12
7) Untreated Check*	--	55 ab	37 ab	43 ab	72 a	45 a	33
							NS

Means within columns followed by the same letter are not significantly different (P>0.05); Protected Least significant difference test (LSD).
NS = not significant. Percentage data were transformed using arcsine transformation. Untransformed means are presented
*All seed was treated with the fungicides Maxim 4FS/Apron XL 3LS/Streptomycin at 2.5, 7.5 and 2%V/V grams AI / 100 kg seed, except the untreated check which received no fungicide or insecticide treatment.

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ACKNOWLEDGEMENTS

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@umn.edu
Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Division,jeanne.ciborowski@state.mn.us
Suzanne Wold-Burkness, Department of Entomology, University of Minnesota, woldx018@umn.edu

The Newsletter is published weekly from May through August, cooperatively, by the Minnesota Department of Agriculture (MDA) and the University of Minnesota (U of MN). Reports are posted on the U of MN and MDA web sites on Fridays. If you have suggestions and/or comments, please send your contributions by 4 p.m., Tuesday to Jeanne Ciborowski, 651-297-3217, jeanne.ciborowski@state.mn.us , MDA, 90 W. Plato Blvd., St. Paul, MN 55107-2094. You can access the Newsletter at the U of MN web site in htm. format at: www.vegedge.umn.edu/MNFruit&VegNews/mnindex.htm and at the MDA web site in pdf. format at: www.mda.state.mn.us/biocon/fruitreports/default.htm

Partial funding for this publication is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association and the United States Department of Agriculture – Risk Management Agency (RMA) and the RMA Community Outreach and Assistance Partnership Program. These institutions are equal opportunity providers.

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Last Revised June 11, 2004.
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