Some Tips for Cover Crop Planting, Establishment and Management

Interest continues in new cover crops for nematode suppression, improving organic matter, and reducing replant problems in horticultural crops. Did you try growing some different cover crops this season? We did. Here are some tips and tricks we have learned from growers and from test plots.

The goal with all the cover crops is to establish actively growing, pure stands of these cover crops. Planting and establishment must be focused on getting a dense stand and achieving the most top growth possible. Nematode suppression from cover crops is dependent upon a consistent, dense, weed free, actively growing cover crop.

• Mustard cover crops provide nematode suppression when the fresh green crop residues are incorporated and break down in the soil. The more plant tissue, the greater the nematicidal action.
• Pearl millet and marigolds, as well as some hybrids of sorghum-sudangrass provide control mostly because they are non-hosts for nematodes. With these crops, it is very important to control weeds, because many weeds are good hosts for nematodes.

Establishing cover crops

Pearl millet, sorghum-sudan, mustard and marigold are all small seed and careful planting is important. Soil should be worked to give a fine, level seedbed in good condition. All of these seeds will have problems getting through a crust.

Seeding rates are:

• Pearl millet - 12 kg/ha (10 lbs/A)
• Sorghum-sudan - 12-40 kg/ha (10-36 lbs/A)
• Mustard - 6-7kg/ha (5-6 lbs/A)
• Marigold - 1.3 kg/ha (1.1 lbs/A

Drilling is the best option for seeding, both depth and distribution are more controlled with a drill, and this is critical under dry soil conditions.

If a drill is not available, broadcast the seed either with a spinner spreader (cyclone) or a seed fiddle - the key is an even distribution of the seed. Use a slightly higher seeding rate when broadcasting. To improve distribution you may want to halve the rate but spread twice. If the seeding rate adjustment is coarse, add some inert material like rice will help the flow and distribution of seed.

Consider seeding mustard twice. Plant mustard as soon as possible in the spring and then work it into the soil as soon as it starts to bolt. Re-seed a few weeks later. The second seeding could be tricky because soils are usually dry in July or early August. For the second seeding ensure that the site and all equipment is ready and be prepared to seed when rain is imminent or soil moisture conditions allow.

Marigold is particularly difficult to seed - the feathery tails get a static charge and stick together and to everything. In previous projects with marigolds, rice helped the seed flow considerably.

Incorporate and firm the seedbed - The key to good establishment is to have good seed to soil contact without burying the seed too deeply. Millet and sorghum-sudan can take being ½ inch deep or a bit more as long as the soil does not crust. Mustard should be in the top ½ inch. In test plots we have run over the area with an ATV. Another alternative is to lightly harrow (we usually flip the drag harrows we have upside down) and follow with a light packer.

Fertility

For nematode suppressing cover crops, nitrogen is needed to ensure optimum growth. Apply at least 50 kg/ha of actual nitrogen. If manure or some other organic source of nitrogen has been applied to the site this year, adjust the nitrogen rate accordingly.

Mowing

Both pearl millet and sorghum-sudan grow very tall, and mature crop residues become difficult to incorporate and breakdown. Pearl millet and sorghum-sudan should be mowed periodically as they reach 3 ft (1 m). Do not mow closer than 6 inches (15cm) or they will not consistently re-grow. Mustard generally does not take traffic or mowing well - work it into the soil when it starts to bolt and flower.

Weed management

Controlling weeds is very important to achieve maximum nematode suppression. If weeds like ragweed, pigweed and lambs-quarters are allowed to grow, they will support and possibly increase nematode populations. Using the stale seedbed technique will greatly reduce weed pressure. This means that the sites should be worked several weeks before seeding, and weeds allowed to germinate over several weeks. Just before planting, weeds can be killed down by Roundup, Ignite or Gramoxone. Seed can be direct drilled or spread on top. Harrowing may be necessary to get seed-soil contact, but this tillage will bring new weeds to the surface. Where drilling is used, and if weeds emerge before the crop, Gramoxone or Ignite could be used to kill off existing weeds (Note: using a plate of glass on the soil surface will give you a couple of days notice on when the cover crop will emerge.)

Herbicides

For sorghum-sudangrass and pearl millet, postemergent herbicides could be used. See Publication 75, Guide to Weed Control under Forage crops. Pardner @ 1 L/ha or 2,4-D @ 0.5 to 1 L/ha can be applied after the crop reached 4 leaves. Pardner is stronger on lady's-thumb and ragweed. Basagran or Peakplus can be used at an earlier stage of growth. There may be some recropping issues with Peakplus - it has a 22 month interval for alfalfa. There is nothing registered for mustard or marigold cover crops, however, research is in progress.

For more information on cover crops, establishment and nematode control visit the OMAFRA website.

Learn more:

• Cover crop information
• Fruit Production Recommendations, Pub 360 - Chapter 4