In response to this, it is extremely important to keep up on fungicide sprays. You must take a preventative approach with this one. Some of our other diseases we can take a wait and see attitude (sort of), but it's critical to be preventative with late blight.
Listed below are some of the labeled products for late blight control for home gardeners:
- Fixed copper
- Daconil or Fung-onil (active ingredient is chlorothalonil)
These should be applied regularly, and the user should refer to the product label for rates, PHI, and safety precautions. These products, as mentioned earlier, will not function well if pressure is high or if disease is present before spray programs are started.
Listed below are cultural controls that can prevent or delay the fungus (information from OAK blog:
- Grow potatoes and tomatoes in areas with good air circulation and well-drained soils. The fungus only infects wet tissue.
- Use certified seed potatoes and resistant varieties, where possible. The fungus can survive in potato seed pieces, but is not spread by tomato seeds.
- Separate plantings of potato and tomato in space and time.
- Promote air circulation to keep leaves dry. Plant in wide rows, oriented with prevailing winds. Stake and prune tomatoes. Control weeds.
- Hill potatoes with high hills to protect tubers from infection.
- Water the soil, not the leaves, to prevent leaf wetness.
- Avoid over-supplying nitrogen. Lush growth is more susceptible to late blight. Scout regularly. Destroy infected plant tissue and plants surrounding infected spots.
- Let potato vines die back completely before harvest. Do not harvest tomatoes when foliage is wet.
- Destroy culled tomatoes and potatoes. Store potatoes and tomatoes from diseased fields separately from those from uninfected fields.
If you suspect late blight, please let me know so we can get it sent to the lab for confirmation.