Was this a BIG weed year for you too? Were the weeds taller than your crops reducing your harvest volume? At the 2011 New England Vegetable & Fruit Conference, Bradley Majek of Rutgers University shared his experience with weed management in a low till program. ”Field weed management is crucial for the first four weeks of growth for most crops, six weeks of corn plants and eight weeks for other late canopy crops, including many vegetables.” If farmers cannot manage weeds for these time periods, harvest yields will be impacted.
Weed Control
Majek discussed four main types of weed control.
1. Biological Control
Typically this means one insect species works to control, not eliminate, one weed species. This type of weed control makes the least sense on cropland and rangeland. Extreme caution must be used with releasing biological control insects. The target weed must be a weed in all forms in all places. One potential risk might be a dandelion which many treat as weeds while others seed special dandelion varieties as part of mesclun salad green blends yielding $10 million in farm revenue in New Jersey.
2. Mechanical Control
Plows, disks, hoes and other tools can help remove weeds in fields. Soil profiles are disturbed and new weed seeds are exposed. Repeated tillage at 7 to 10 day intervals removes foliage, encourages regrowth and depletes root’s carbohydrate stores weakening plants. Risks include damage to soil structure, increased compaction or erosion risk, organic matter oxidation and loss as well as the decreased nutrient-holding capacity and water penetration. Other considerations are the high cost of labor and fuel.
3. Horticultural Control
Mulches, cover crops, crop rotation and stale seedbeds are all means of horticultural control. Most important is prevention of new seed formation by preventing weeds from setting a new crop of seeds.
4. Chemical Control
While this is the easiest control from some perspectives, it can have significant impacts on farming practices. Often this choice offers more complete weed control at a lower cost than with other techniques, but should not be used instead of good horticultural practices such as crop rotations and the use of cover crops. Herbicides should be carefully chosen for weed control without impacting future crops or the environment. There are pre and post emergent treatments as well as residual, non-selective or growth regulator products. Glyphosate is a non-selective herbicide, generally applied with warm temperatures when weed plants are in full bloom to the green fruit stage of growth.
Crop rotations can reduce disease and insect pressured and improve soil fertility and tilth. Horticultural, soil and pest control benefits include utilizing nutrients and soil moisture. Legume crops in the rotation can increase soil fertility through nitrogen fixation. Alfalfa’s deep tap roots penetrate and loosen compacted soils and hard pan. Through root renewal and tilling perennial grass and hay crops increase organic matter and improve soil structure.
Crop rotation can offer a welcome impact on disease and insect pressure. Weed impact is less obvious. A regularly plowed and tilled field will eventually exhaust the seed bank of winter annuals that bloom and set seed in late spring.
Crop rotation can help control difficult weeds like Canada thistle or yellow nutsedge. Certain crop combinations allow targeted weed(s) to be sprayed multiple times. Other crops can be planted to shade or smother the weed(s) during bloom and seed set reducing weed pressure over time.
To control Canada thistle with its deep wide roots, use tillage, a glyphosate product, Stinger or Basagran to prevent the weed from emergence in the spring, during bloom in early summer and through the fall on the second growth spurt. For example, till and plant early season snap beans treated with Basagran followed by fall broccoli treated with Stinger in year 1; the next year plant sweet corn treated with Stinger, followed by a glyphosate product in early fall. In year 3 plant matted row strawberries treated with Stinger.
Yellow nutsedge with its tuber forming spreading rhizomes and vigorous growth is the most prolific weed of horticultural crops worldwide. To control yellow nutsedge, late summer tuber formation must be prevented for several years. Effective crop rotation with early summer harvest allows tillage to keep the field nutsedge free during the late summer tuber formation period.
The herbicides Dual Magnum, Basagran and Sandea are the most effective on yellow nutsedge. One example of crop rotation is effective: plant early cucumbers treated with Sandea, followed by late summer snap beans treated with Dual Magnum and Basagran in year 1; the next year plant tomatoes treated with Sandea. In year 3 plant, early sweet corn treated with Dual Magnum and Basagran followed by tillage and pumpkins treated with Sandea in year 4. This plan prevents yellow nutsedge tuber production and can reduce this weed population to minimal levels that can be managed by cultivation or hand weeding.
Be sure to follow all label schedules for elapsed time before replanting with residual herbicides. Refer to the Commercial Vegetable Production Recommendation guide for plant back restrictions to plan crop rotations and weed control programs BEFORE applying herbicides! Consider herbicides without plant-back restrictions (or very short periods) or herbicides labeled for used on planned succession crops.
When using an early cucumber crop treated with Command and Sandea you should get excellent weed control; late summer crops would be limited to snap beans that year. Using Prefar instead on the cucumbers would yield less weed control, but more late summer crop options would be available. Lettuce, onion, cole, parsley and summer squash or a second cucumber crop (not recommended) are acceptable options shown on the Prefar label.
Local Cooperative Extension agents are available to help you plan crop rotations.
For additional information, contact Dr. Bradley Majek via email or at Rutgers University, Rutgers Agricultural Research and Extension Center, 121 Northville Road, Bridgeton, NJ 08302 or call (856) 455-3100.
You can see Majek’s contribution “Using Crop Rotations to Manage Weeds” to the NE Vegetable & Fruit Conference proceedings starting on page 4.
A similar story was published in the January 16. 2012 New England edition of "Country Folks."
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