Finding a nice-sized zucchini was a pleasant surprise, what with our up and down summer. I leaned in closer (feeling a little proud), when my balloon burst. I saw a gray color — not normal for a green zucchini. It was my first clue that something was in the air.
Something was in the air alright. It was mold. Ick.
Yes, after a couple weeks of blessedly calm weather mixed with fog, conditions were perfect for gray mold to explode on zucchini fruits, tomato leaves and anything else standing in its way.
Gray mold (Botrytis cinerea) is found on a wide range of plants. If I were to list them all in this column, you’d be reading nothing but scientific names from here to the end.
No garden is immune. Gray mold is a fungal disease that travels quickly through gardens, infecting plants in outside beds as well as in enclosed spaces such as greenhouses and hoophouses. Cool, damp weather is the perfect storm for gray mold.
How do you identify gray mold? It appears as soft, mushy spots on leaves, stems, flowers and on store-bought produce. Given the right conditions, the mushy areas often become covered with a coating of gray fungus spores.
The disease easily affects plants that are already damaged or beginning to die. It then spreads quickly and can cause extensive damage to healthy parts of plants. So if you’re one of those tomato growers who can’t resist pinching and trimming suckers and leaves, then be gray mold aware.
The appearance of gray mold is not limited to garden plants, however. You’ve seen this culprit before: on store-bought strawberries, oranges and inside heads of lettuce. Have you sliced through a head of romaine lettuce only to see and a cloud of gray mold erupt?
It gets better. Gray mold can overwinter on plants, even in the soil, which is why it’s so important to clean out seedling containers and greenhouse interiors at the end of the season.
Spores develop when conditions are optimal, and they are transported by wind, hands, tools, clothing or splashing water onto blossoms or young leaves, where they germinate and enter the plant.
Spores require cool temperatures (45 to 60 degrees) and high humidity (around 93 percent) to germinate. Which means, during periods of drizzle and fog, make a special effort to check your plants. Carefully and often. Molds, like aphids, don’t happen overnight.
That’s all good information, Marion, but how do I prevent and stop gray mold?
Glad you asked!
It sounds like a science fiction movie script, but gray mold exists most everywhere — in the air, on surfaces — just waiting for the right conditions to “bloom.” Whether you’re transplanting seedlings, watering a hanging basket or taking care of someone else’s houseplants, these tips will help prevent a mold infestation:
• Remove faded flower blossoms and fallen petals. As you do this, though, be aware of spreading spores. Move slowly and dip your hand tools now and then into a mild ammonia-water or essential oil-water solution. In the greenhouse, where it’s common to grow tall sunflowers and poppies, this means cleaning up petals that fall onto plants or soil below.
• In the vegetable garden, remove infected plants immediately after harvest. Plant tissues that are stressed, crimped, ripped or not actively growing are great hosts for gray mold to find a footing. Rhubarb plants are especially susceptible to mold at the end of the season.
• Improve sunlight and increase air circulation, and don’t crowd plants. Here’s the thing: In greenhouses and hoophouses, the less air circulation you have, the greater the chance of developing mold.
• Heads up: Vents that open automatically on hot days are not enough. You need fans to run 24/7. One of my favorite ways to increase air flow in the hoophouse is to hang an oscillating fan upside down and let it spin back and forth, back and forth. Efficiency by randomness.
• On overcast days, do NOT close your greenhouse doors and windows thinking you need to preserve heat. Elana White of Strawberry Fields Nursery told me years ago that shuttering up your plants in cool, calm air is the worst thing you can do.
• Avoid overhead watering, especially late in the day. Keeping foliage dry is extremely important to control this disease, so avoid overhead watering and overwatering.
• Clean the greenhouse and the hoophouse as best you can at the end of the season. Remember, gray mold can overwinter in the soil, in decaying plant debris, and on infected dead plant material.
• Sterilize plant containers with a mild bleach or vinegar solution before re-using them. At the very least, rinse them well after use and air dry them thoroughly.
• If you want to control gray mold, your first defense it to keep your plants healthy, preferably with organic growing methods.
Meanwhile, here is a lovely quick bread for celebrating our upcoming berry picking season:
Lemon Raspberry Bread
6 tablespoons soft butter
1 cup sugar
1 1/2 cups flour
1 tsp baking powder
1/4 teaspoon salt
1/2 cup milk
Grated rind of 1 lemon
3/4 cup fresh raspberries
Preheat the oven to 350 degrees. In a medium bowl, sift flour, baking powder and salt. In another bowl, cream butter, lemon rind and sugar. Add eggs and mix well. Add the dry mixture to the creamed mixture alternately with the milk. Fold in raspberries. Turn into a prepared 5x9 inch loaf pan.
Bake for 50-60 minutes or until a toothpick inserted in the center comes out clean. For the glaze, stir together powdered sugar and lemon juice. After removing the bread from the oven, pierce it all over with a fork or toothpick. Spoon lemon glaze all over the top. Cool 15-20 minutes before turning out onto a rack.