SR9090 - Integrated Crop Management of Onion White Rot

Researcher:

Dr. Mary Ruth McDonald, Dept. of Plant Ag., University of Guelph, Kettleby

Objectives:

To improve the management of onion white rot on onions grown in organic soils through the use of biological controls and resistant cultivars, alone and in combination with fungicides. Effects of the treatments on disease incidence and onion yield will be considered.

Expected Benefits:

1. Benefits to onion growers will be:
   a) lower crop losses
   b) improved quality
   c) more stable export markets
   d) the ability to follow a regular crop rotation program to reduce overall damage from insects, diseases, nematodes and weeds.
   

2. Packers, shippers and exporters of onions will benefit from having improved quality of onions to work with and more reliable yields and quality from year to year.
   

Summary of Research Results:

Research conducted in the Bradford area has shown that commercially available formulations of mycorrhizae can effectively reduce the amount of white rot on onions. Good results were achieved when onion transplants were grown in soilless mix containing the mycorrhizae. At harvest, untreated onions had 30% white rot, while those with mycorrhizae had 15%, as did onions treated with an experimental fungicide. The level of disease control was related to the proportion of roots colonized by mycorrhizae.

However, most onions in Ontario are direct seeded, so research turned to applying mycorrhizae on the seed or in the seed furrow. While levels of disease in the field were too low to provide a good test of the mycorrhizae, the trials did show that the level of inoculum on the seed was important. There was better colonization of the roots when each seed had an average of 75 colony- forming units of the beneficial fungus. Another important result was that the addition of the experimental fungicide appeared to increase, rather than decrease the amount of root colonization by the mycorrhizae, suggesting that a combination of the two controls might be even more effective.

These trials were conducted on two onion cultivars: Fortress, which has shown some field resistance to the disease, and a susceptible line. Fortress held up well in the tests, and also had a higher rate of root colonization, suggesting that naturally- occurring mycorrhizae may play a role in resisting or suppressing disease on some onions.

Research is continuing to test mycorrhizae applied to the seed furrow and to the seed, in addition to screening more lines for field resistance to white rot.

The two commercial formulations of mycorrhizae tested in these trials are MIKRO-VAM7 and PROMIX PGX7 with MYCORISE7 1000. These are available in Ontario and they don't need any further registration in order to be used. PROMIX PGX7 with MYCORISE7 1000 is a soilless mix with the mycorrhizae in it, it is produced by Premier Tech. For more information call 1-800- 667-5366 or 1-800-606-6926. MIKRO-VAM7 is a VAM (vesicular-arbuscular mycorrhizae) ready to add to the soilless mix. It is produced by Mikro-Tek. For more information call (705) 268-3536.