News from Southern Minnesota

(Hollandale Area)

By Jim Tjepkema, Agric. Consulting Services, Clarks Grove, Minn.

Weather:
Excessive rainfall was a problem again this year. Rain during planting season lead to unusually late planting dates for some fields and to water damage in some other fields that were planted early. Heavy rain later in the season flooded many fields causing more water damage. A few fields suffered from very extensive water damage. As the weather improved toward the end of the season some fields seemed to recover from water related problems. A week of very warm weather in the middle of the season appeared to favor onions resulting a sudden burst of growth in this crop. According to Dave Ragsdale, an entomologist at the University of Minnesota, the week of very warm weather created conditions unfavorable to aphids and these pests caused little or no problems in the 1999 growing season. Unusually dry fall weather result in favorable conditions for harvest.

Drainage and Compaction:
Most of the soils used for vegetable production in our area are naturally slow draining due to their very high organic matter content. This year some fields seemed to drain very slowly and stayed wet for a long time. In these slow draining fields the movement of water downward into tile lines apparently was very slow or completely blocked. It has been suggested that excessive tillage may have had a negative effect on soil structure needed for good downward movement of water. Crop rotations that include plants with large fibrous root systems may help improve drainage by improving soil structure. The only crop with a large fibrous root system that is used in current vegetable crop rotations is sweet corn and this crop is not part of the rotation in all fields. Observations on drainage during 1999 seemed to indicate that changes in tillage practices, crop rotations, or other management practices may be needed to solve problems with very slow drainage. High organic matter soils are resistant to soil compaction and can be worked when they are somewhat wet. However, problems with compaction were observed in the spring of 1999 in onion fields and some other fields. The compaction problems seen in 1999 were similar to problems observed in other years with very wet early spring conditions. If the soil is too wet at planting, it may become compacted greatly reducing the downward movement of water. Water held near the soil surface by compaction may evaporate and leave behind a thin white layer of salt that could be seen in some fields this year. This year, and in other years, the crops in compacted fields grew very slowly and fell behind the same crops planted later under drier conditions.

Insect Pests and Plant Diseases:
I am very happy to report no detection of late blight in potatoes in our area in 1999. Early blight was a problem in potatoes as it is every year, but control of this disease was very good in many fields. Apparently the newly available fungicide, Quadris, was responsible for holding down the spread of early blight. Quadris is know to be very effective against early blight and it was widely used for the first time this year. Some fields stayed very green up to the end of the season. White mold was found in small patches in some fields where potato vines stayed green due the good control of early blight. Botrytis was detected early in the season in onion fields. Fungicide used this year for control of Botrytis appeared to work very well as there were no serious problems with this disease. The biggest disease problem in onions was soft rot that was found in fields that were hit by heavy rain or hail. There were minor problems with leaf blight in carrots that were probably caused by wet weather. As usual, a slight amount of aster yellows was found in carrots. As already mentioned, aphids caused little or no problems in potatoes this year. However, the potato leafhopper and Colorado potato beetle did require treatment. The numbers of PLH were fairly high and CPB was found in many fields. Problems with CPB seemed to increase this year although there were many fields where these beetles were only a minor problem or not a problem at all. Variegated cutworms, which are usually not a problem, became problematic this year in a few fields where they damaged vines and chewed holes in tubers. No unusual insect pest problems were found in carrots or onions. Onion maggots were a minor problem in a few onion fields. Very few onion fields needed treatment for thrips. As in the past, multiple insecticide treatments were needed to control aster leafhoppers in carrots.

Other Production Problems:
Weak potato seed seemed to be a problem in some late-planted fields. Apparently some of the late planted seed was held too long under poor storage conditions. When planting is delayed, it may be desirable to move seed to a good storage facility if one is available. Loss of nitrogen for crop production is usually a problem in years with excessive rain fall and flooding. This year many potato fields turned somewhat yellow indicating that they were deficient in nitrogen.

Editors Note: Future issues of the Minnesota Vegetable Newsletter may include more updates from Jim and southern Minnesota. Readers can also subscribe to his newsletter (published 4-6 times/year) by contacting Jim directly:

Jim Tjepkema Agric. Consulting Services
P.O. Box 128
Clarks Grove, MN 56016
(phone: 507-256-4876)

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@tc.umn.edu
Jeanne Ciborowski, IPM Program, Minnesota Department of Agriculture, jeanne.ciborowski@state.mn.us
Production Editor: Suzanne Wold, Research Specialist, University of Minnesota, woldx018@tc.umn.edu

Disclaimer
Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current directions of the manufacturer

Last Revised January 20, 2000.
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer.©1999 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.