Growing and maintaining a garden can be equal parts rewarding and frustrating. Just when you think your green babies are thriving, a streak of bad weather, a pest invasion, or an innocent mistake on your part (over-watering or under-watering being prime examples) can erase months of effort.
And then there are plant diseases which can wreak havoc like a trained assassin: quickly and undetected. One leaf starts to look a little off, and just like that, the entire plant is ravaged.
We spoke to Dr. Jim Farrar, Director of the University of California’s Statewide Integrated Pest Management Program. He offered up some tips on how to spot, treat, and most importantly, prevent, some of the most common plant diseases you might come across in your garden.
A wide variety of crops are susceptible to this common affliction that strikes early in the planting process. Damping off usually occurs when soil is too cold and wet or if seeds are planted too deep.
“Fungi live in the soil that will attack and kill germinating seeds before the seedling becomes established,” says Farrar. “The seed may be killed underground or the seedling may come up above ground and die and fall over, but it never gets to be an established plant.”
When you’ve accepted that your little plants aren’t going to make it, take a look at what went wrong. “If you dig them up, you’ll see that their roots are discolored. Usually dark colored and sort of mushy,” Farrar says. “[Healthy] roots are very light colored and not mushy.”
If you experienced damping off, he recommends trying again when the weather is warmer. And, his general rule when it comes to planting depth is roughly twice the size of the seed.
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Here we have another root problem, but this fungal disease occurs in well-established plants. As for the signs, look for wilting and yellowing leaves. “The leaves turn necrotic and die,” says Farrar.
Over-watering is the primary factor so whether you’re in a humid region that gets hit with several days of rain or an arid climate and erred in over-irrigating take caution.
Other than cutting back on watering or singing “Rain Rain Go Away,” Farrar’s preventative tip is to plant on raised beds to keep the roots a little higher.
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You can also add some calcium to the soil with gypsum. Topping it off with compost is another method. “It lightens up the soil so the soil isn’t prone to get saturated quite as easily,” per Farrar.
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“Serious stuff” is how Farrar describes the disease that played a significant role in the Irish potato famine.
A tell-tale sign of the fungal disease which lurks in the soil is yellow lesions on the leaves, particularly the lower ones underneath the canopy which don’t dry out like the ones on top with plenty of sunlight.
Treat late blight by clipping off affected leaves as soon as you spot them. You may end up with a less impressive crop yield at the end of the season, but at least you’ll still get something for your troubles.
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Farrar recommends taking preventive measures by spacing out your plants as much as you can. That way, they can adequately dry out between rain spells and watering.
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Much like late blight, this fungus attacks the leaves and creates yellow lesions that expand over time. “Eventually the leaf does die, but it takes longer for it to happen than with late blight,” notes Farrar.
If you suspect downy mildew is in your midst, Farrar suggests channeling your inner Sherlock Holmes by grabbing a magnifying glass and checking underneath the leaves. Its presence will be obvious: “You’ll see fungal structures that look like tiny little trees,” he says. “The spores look like tiny little lemons.”
Downy mildew is airborne, making it a challenge to prevent. While your plant obviously needs water to grow, wet leaves are catnip to these spores. Try to keep the leaves as dry as possible. Fertilize, but not too often as too many nutrients can result in soft foliage that is susceptible to fungal growth.
At the end of the season, Farrar recommends doing a thorough cleaning of your garden’s top soil. If there’s plant matter resting on top, it leaves an opening for downy mildew spores to gather.
Though, like other diseases, tiny yellow spots will be the first indication that trouble is afoot, over time a distinctive calling card will affirm that powdery mildew is present. Eventually the spots will expand into powdery spores (hence the name) that coats the leaves.
To prevent and treat powdery mildew, Farrar again suggests the two-pronged approach of sanitation and spacing. “Clean up your garden at the end of the season,” he says. “Don’t leave a lot of wasted green on the surface. Give plants enough space so that they aren’t really crowded and trapping humidity of the canopy of the plant.”
Final Tips for Better Luck Next Year
“Plant once the soil is warm enough for the particular kind of crop that you’re trying to grow,” Farrar cautions. “Don’t plant too early in the spring.”
“Plant into well-draining soil that has had some organic matter incorporated into it,” he adds. “Give plants enough space so that they can dry out if there’s rain or high humidity.”
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