During hot, dry summers like this one, timely weed management and retention of surface mulch can help reduce crop stress and minimize irrigation costs, says Dan Brainard, Michigan State University horticulturist, looking back at lessons learned.
Many weeds are voracious consumers of water. For example, large crabgrass and common lambsquarters use over 80 gallons of water to produce one pound of plant tissue.
Evidence from MSU trials in asparagus suggests that such thirsty weeds may deplete soil moisture by as much as 0.5 inch per week in the heat of the summer. Under these conditions, timely removal of weeds reduces irrigation costs and improves crop yields.
Under reduced tillage systems, rye or wheat cover crops left on the soil surface can be very helpful for conserving soil moisture.
For example, in MSU strip-tilled sweet corn trials, plots with rye residue on the soil surface had approximately 5 percent greater water content in the top 10 inches then plots without rye mulch. This is equivalent to about 0.5 inch of irrigation savings.
Brainard says the combined effects of weeds and mulches have been very noticeable in winter squash research trials this year. Where crabgrass is present, winter squash plants wilted noticeably within two days of irrigation.
In contrast, where weeds are effectively controlled with cultivation and herbicides, winter squash is relatively unstressed.
The least-stressed plants are those that were planted into a winter rye residue using a strip-till system. Good weed control combined with mulch can conserve up to one inch of water per week during warm summer periods.