cucumber-diseased-leaves_blkforest-co_lah_6767-1My cucumbers are sick. As far as I can tell (although I’m not 100% certain), they’re suffering from something called Alternaria Leaf Blight. But no matter what the particular fungus is, the leaves have expanding brown spots and are beginning to yellow and die, starting from the roots and working their way upward. New fruit is being aborted. It’s sad—very, very sad.

I don’t often have to contend with diseases in my garden. Good horticultural practices lead to healthy plants, and healthy plants resist disease. However, given our erratic weather and cold nights, I grow my cukes in my little greenhouse. Because options are so limited, I plant them in the same spot year after year. Even though I renew the nutrients in the soil, fungal spores accumulate, and now I’m dealing with the unhappy result.

Identifying the problem is the first step to control.

I pored over a variety of university websites before I was satisfied that my plants had Alternaria. (This time the University of Minnesota’s extension site proved the most helpful.) I prefer to use sources like extension because their information is based on scientific research—and they aren’t trying to sell me anything. I know the information will be accurate and up-to-date. If you don’t feel up to solving the riddle on your own, try calling your local master gardener help desk or county extension office. They’re there to help.

Once I knew what disease I was dealing with, I could read up on treatment options. In this case, a copper spray is recommended. Since we’re nearing the end of the growing season, spraying is probably not worth my effort and expense. We’ll eat the last of the plentiful harvest we already have and call it a year.

However, I want to do what I can to avoid a re-infection next year. How did my plants get infected in the first place? According to the Minnesota fact sheet:

Alternaria cucumerina can be carried long distance on wind currents and can be spread within the field by splashing water. Wet rainy weather favors diseases, and damage can be very severe in warm, wet conditions. The fungus survives from season to season in plant debris.

cucumber-diseased-leaves_blkforest-co_lah_6764Growing in a poorly-ventilated greenhouse, my cucumbers were certainly exposed to warm (very warm!) conditions. Plus, whenever I water, the humidity skyrockets. While I have a drip system in place to irrigate my plants, one of my soaker hoses developed a crack—so I turned off the system and watered by hand until I could get to the store and buy more tubing. I’m sure I inadvertently splashed soil onto the leaves.

Then, I waited until spring to clean out last year’s dead vines. By that time, they were crispy, with the leaves turning to powder as I pulled them from the trellis. And yes, I reused my nylon trellis, too. Oops.

So… what have I learned?

  1. Ideally, I’d move my cucumbers (and any other plants in the squash family) to a new location on a three-year rotation, giving the spores in the soil time to die. I can’t do that in a 10 by 11 foot space, but I can swap them with my tomato plants. It’s at least a step in the right direction.
  2. I will make sure my drip system is working. Plus, I’ll add a thicker layer of mulch under the plants to keep soil off the leaves.
  3. I’ll remove and destroy the infected plants. They’ll have to go to the landfill instead of the compost pile. I’ll make sure any fallen leaves and raked up and disposed of as well.
  4. I’ll spring for a new nylon trellis, or take this one down and soak it in a 5% bleach solution before reusing it.
  5. Since my cukes are under glass, they don’t get rained on. If they were in the garden, I’d make sure to avoid touching the leaves while they are wet. That’s good practice no matter what crop you’re growing.

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