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Drought Thoughts  

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Corn News

Wheat News

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Weed Management Under Drought Conditions

   Weed control is important during drought. Low soil moisture increases weed competition with the crop for moisture. Poor weed control will cause problems in future years through the weed seeds produced. Cultivation of row crops remains an option for weed control during dry conditions. Benefits would be minimal where weed control is satisfactory and the soil surface is not crusted. A shallow cultivation can effectively control small weeds and loosen crusted soil.

   The dust mulch provided by cultivation can also help slow evaporation of water from the soil. Cultivation can cause the loss of a small amount of soil moisture only if cultivating to soil moisture depth. This moisture loss, however, is minimal compared to potential water losses due to weeds. Harrowing or rotary hoeing will also remove small weeds and break up surface crusts.

   Soil applied herbicides are less active under drought conditions. This is especially true of preemerge herbicides which require rainfall to move them into the soil where weed seeds germinate. How soon after application rain is needed and the amount required is dependent on the particular herbicide used, soils and environmental conditions. A harrowing or rotary hoeing can help incorporate herbicides and remove escaped weeds where adequate rainfall has not occurred.

   Post emerge herbicides perform best when weeds are actively growing. High temperature, high relative humidity and adequate soil moisture are ideal. Drought stress of weeds reduces herbicide effectiveness. Weeds are not able to grow as rapidly with limited moisture. Herbicides affect processes that occur when the plant grows. Weeds develop a thicker wax layer, or cuticle, on their leaves to help reduce moisture loss during dry conditions. This can reduce the ability of post emerge herbicides to enter weed leaves. Common lambsquarters are especially effective at developing thick cuticles and therefore difficult to control. Herbicide adjuvants help overcome the weed leaf's resistance to herbicide penetration. The selection of the proper adjuvant can improve weed control under drought stress conditions. Individual herbicides may require different adjuvants for best performance. Choose tank mixes that have compatible adjuvants under drought conditions. Separating grass and broadleaf herbicides will help prevent loss of grass control due to herbicide antagonism. Reduced herbicide rates are less likely to perform well under conditions of weed stress.

   Dry soils after herbicide application can increase the chance of carryover. Soil moisture is essential for microbial and chemical breakdown of herbicides. A period of dry soil conditions can reduce herbicide breakdown and cause injury to the following crop. Weed control during drought conditions requires additional management and flexibility on the part of the producer. Herbicide programs and cultivation may need to be modified to provide acceptable weed control. Always read and follow herbicide label directions to maximize weed control and minimize injury to the current or following crop.

   Copyright © 1998 by University of Minnesota Extension Service Updated September 14, 1998 mfox@extension.umn.edu

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 1930 Dust Bowl Clouds


The clouds appeared on the horizons with a thunderous roar. Turbulent dust clouds rolled in generally from the North and dumped a fine silt over the land. Men, women and children stayed in their houses and tied handkerchiefs over their noses and mouths. When they dared to leave, they added goggles to protect their eyes. Houses were shut tight, cloth was wedged in the cracks of the doors and windows but still the fine silt forced its way into houses, schools and businesses. During the storms, the air indoors was "swept" with wet gunny sacks. Sponges were used as makeshift "dust masks" and damp sheets were tied over the beds. 

Harlan Jacobsen Editor 

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We have done a lot of research on drought, looking at it as it has happened in the past down through the centuries, and try to pass along to you what is important and useful to your ag success. One of the things you learn is that drought happen on a regular cycle. Short droughts in the cornbelt happen once every 12 years. Long droughts (several years.) happen on a 25–year basis and cover a wider area. 

   Many of these over the centuries have lasted from 10 to 20 years. The dust bowl 30's drought lasted seven years from some reports and others say eight years. Compared to some from long–term past, it was relatively short. So to be determined (since both hit together for this drought) is this a short–term one– or two–year drought from the 12–year cycle or is this a 10–year or longer drought. 

   Whichever it is, it may be around next growing season as well or even longer. The Texas drought has been going on for eight years so these folks have been through what the cornbelt farmer is dealing with for the first time in this generation in this growing season. They have learned to live with it and many have adopted what is known as conservation tillage. 

   We have included information on how this is working in this issue, realizing Texas has some differences such as year–round weed growth. However, much of conservation tillage residue systems and low tillage come from methods that have been accepted in the Midwest for years. The result of this under actual drought conditions over a long term is what we are pointing out in the Texas success stories. 

   Farmers using this in drought areas find it offers new hope of being in the black during long–term drought conditions. Costs are far less, yields are up, and most are sticking with it. Conservation tillage basically is a system of keeping residue on the soil service and reducing or eliminating plows and other tillage equipment. Your editor recently visited a central Iowa farm that is using a modification of this (before drought) and reported the spread of earth worms with no tillage was remarkable ( killed off by normal tillage methods.) and photos of his fields make it easy to identify exactly how far the worms have spread in a period of two years. 

   Reports are the soil is like a sponge in worm areas and soaks up every bit of moisture. Plant roots are able to follow the worm holes and go deeper down then with plowing. The worms thrive on surface residue which is retained on the surface. Planting is right down through the residue, and fertilizer is added with special syringe–type machinery that places it below the residue without disturbing it. Not yet in use in the Midwest is the stalk–puller machinery that pulls stalks out by the roots and places them on the surface residue system (see Texas article and photos). 

   All of this may be of little help this crop year, but you might look into it and gear up for the next season. We have included some warnings over the past months here on insect increases during droughts, and finally have answers why grasshoppers literally explode in numbers during hot dry weather. We have not been able to verify reports that other insects are showing up in record numbers. We would like to receive your comments on what we carry ( choose) that has been most helpful and what you would like to see continue. 

Harlan Jacobsen Editor 



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