Crop differences. Cover crops may differ in their ability to support a population of Trichoderma that is sufficient for colonizing a subsequent crop. The colonization of Trichodermaon several species used as cover crops was examined in greenhouse trials. Six cover crops of regional significance were selected: Annual ryegrass, canola, red clover, grain rye, hairy vetch and winter wheat. The experiment was done twice with comparable results.
Colonization was best and growth most vigorous in annual ryegrass. This cover crop is killed in the winter. Clover was reasonably well colonized, but the root mass was very small compared to the others, so the total inoculum provided may be insufficient. Vetch did not have sufficiently high inoculum to be considered a likely carrier. Rye was modestly colonized, but proved to be a poor vehicle in field tests described in Objective 1. Canola was also modestly colonized, but may overwinter the fungus better. These results suggest wheat as the most likely cover crop to use for carrying over and multiplying Trichodermainoculum, with canola the likely second.
Colonization of various potential cover crops by Trichoderma.
C= uninoculated, T= inoculated with Trichoderma harzianum strain 22.
Good colonization is >104 cfu/g.Recommendation: Colonized cover crops are not an effective way to inoculate sweet corn with Trichoderma. Many cover crops are well-colonized by T-22.
To distribute inoculum throughout the soil, the fungus needs to grow as fast as the roots. In the summer, that is always the case, but the hyphae of Trichoderma slow down when the temperature is below 60°F, and it becomes dormant when the temperature falls much further. Overwintering crops have a lot of root growth when the soil is too cold for active Trichoderma growth. The lack of fungal growth when the cover crop is doing most of the critical expansion through the soil will limit the usefulness of this technique. It is possible that a summer cover crop can be useful for inoculating a later summer crop, but that was not considered relevant for sweet corn in the Northeast. In the future, cold tolerant strains of Trichoderma are likely to be developed. These should be tested on overwintering cover crops and also on fall-sown crops such as winter grains.
Field trials.
Rye cover crop in grower fields. In three field trials, we tested the ability of a sweet corn crop to be colonized by Trichoderma when it followed inoculated winter rye that had been plowed down before sowing the sweet corn. At all three farms, no Trichoderma colonized the subsequent corn crop
Recommendation: Do not expect Trichoderma to colonize crops that follow the crop that was inoculated with T-22.
Colonization of sweet corn roots when sweet corn was planted into the residue of a rye cover crop that had been inoculated with T-22. In grower trials at Minns and Hansen and in an Experiment Station (Vegetable Resarch Farm) trial in 1996, colonization was the same as in uninoculated rye. At Minns, the just-adequate colonization with granules serves as a positive control. Tillage and inoculum placement. We tested whether the placement of the inoculated rye residue affects the colonization of sweet corn. We expect the highest inoculum near the crown of the rye plant. Thus no-till places the corn seed with the highest inoculum, chisel plowing mixes the inoculum more, and moldboard plowing places the inoculum 4 to 6 inches below the seed. None of these tillage methods resulted in colonization above background. We interpret this, and the results of the grower experiments, to mean that there was little or no effective inoculum present on the rye in the spring.
Colonization of sweet corn by T-22 when planted into inoculated or uninoculated rye following 3 types of tillage that redistribute the rye roots in different ways. There was no evidence of inoculation of the sweet corn using this method.
