Time to Plant Warm Season Cover Crops for Nematode Control

Now that the soil and air are both warm, it's time to plant cover crops for nematode suppression. Cover crops like pearl millet, marigold and sorghum sudan (make sure you have the right variety though for the sorghum eg. Sordan 79 or Trudan 8) can reduce nematode numbers in the pre-plant year for strawberries or in preparation for orchard replanting . When cover crops are used to reduce nematodes, the goal 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.

• Seedbed - should be worked to give a fine, level seedbed in good condition - all of these seeds will have problems getting through a crust.

• Seed - seeding rates are

  • Pearl millet - 12 kg/ha (10 lbs/A)

  • Sorghum sudan - 12-40 kg/ha (10-36 lbs/A)

  • Marigold - 1.3 kg/ha (1.1 lbs/A)

• Planting

  • Drilling in the seed would be the best option for planting, as both depth and distribution are more controlled with a drill which is critical under dry soil conditions.

  • If broadcasting the seed - use a slightly higher seeding rate to compensate. To improve distribution you may want to halve the rate but spread twice. Not every seed will fall into good conditions with a broadcast application. Nematode suppression from cover crops is dependent upon a consistent, dense, weed free, actively growing cover crop.

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

• Incorporate and firm the seedbed - The key 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.

• Host range for root lesion nematode - Root lesion nematodes feed on over 500 host worldwide including many vegetable, berry and fruit tree crops as well as several weed hosts such as nightshade, burdock, dandelion and plantain. They will also survive and reproduce in some weed hosts such as ragweed, lamb's quarter and pigweed, however, these plant species are not preferred host for this pest. Weed management is very important in fields planted with nematode suppressive cover crops since the nematodes will migrate to weed hosts on which they feed upon and reproduce, thus negating the suppressive effects of the cover crops.

• Weed management - Obviously controlling weeds is very important to achieve maximum nematode suppression. Where possible, using the stale seedbed technique will greatly reduce weed pressure. This means that the sites should be worked as soon as possible, and weeds allowed to germinate over several weeks. Just before planting, weeds can be killed down by Roundup, Ignite or Gramoxone (or flaming if available). 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 Sudan-sorghum 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 Amine 600 @ 0.5 to 1 L/ha can be applied after the crop has reached 4 leaves.

  • See Table 10-1 to see what weeds will be controlled by each herbicide. For example, 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, but no information on apples.

Related Links

• Pub 75, Guide to Weed Control - forage crops
• Pub 75 - Guide to Weed Control - Table 10-1
• Fruit Production Recommendations OMAFRA Pub 360
• Cover Crop Information, OMAFRA website

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