Guides · Problems
Plant Problems
What’s wrong with your plant, how to be sure, and whether anything you can buy will help.
A page about a plant problem almost always does two things: lists the causes, then names something to spray. On every problem below, one of those two is broken — and which one is the most useful thing we can tell you. Sometimes the list cannot work, because the three caterpillars people call cabbage worms are all green and no color chart separates them. Sometimes the spray cannot work, because the grub is sealed inside the leaf, or because calcium cannot cross into the fruit however you apply it. Each guide starts from what you are actually looking at, says plainly where two causes cannot be told apart by eye, and where the honest answer is nothing now, something earlier in the season, it says that instead of selling you a bottle. Timing question rather than a health one? The frost date lookup is the place to start.
Aphids: How to Be Sure, and When to Leave Them
How to get rid of aphids, and when not to bother. Every aphid has two tiny tailpipes, and Minnesota says most populations can simply be ignored. Here’s when.
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Blossom End Rot: It Is a Calcium Problem, and the Calcium Spray Cannot Fix It
The fruit really is short of calcium. Your soil usually is not. Clemson names the spray as a myth for two mechanical reasons — and the actual fix is how you water.
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Cabbage Worms: Three Green Caterpillars, and You Tell Them Apart by Poking Them
Cabbage worms are three green caterpillars: imported cabbageworm, cabbage looper and diamondback moth. Color won’t tell them apart. Touching them will.
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Damping Off: There Is No Cure, So the Whole Job Is Getting Seedlings Past It Fast
Damping off has no cure, so the job is getting seedlings past it fast. Wisconsin’s advice: germinate warm so seedlings rapidly grow out of the stage.
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Cucumber Beetles: Stripes Mean the Grubs Are in Your Roots, Spots Mean They Are Not
Cucumber beetles: only the striped one’s larvae feed on cucurbit roots, says UC IPM. How to tell striped from spotted, and what a wilting plant means.
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Flea Beetles: When the Shot-Holes Matter and When They Don't
Tiny holes peppered through your leaves, and beetles that jump when you lean in. On a two-week-old seedling that is urgent. On a grown plant it is not.
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Cucumber Leaves Turning Yellow: The Straight-Edged Patches Are the Tell
Cucumber leaves turning yellow in straight-edged patches? It’s downy mildew or angular leaf spot, and the underside of the leaf tells you which.
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Japanese Beetles: Why the Trap Makes It Worse
Metallic green head, coppery wings, leaves eaten to lace. Two extension services find the traps pull in more beetles than they catch. Here is what to do instead.
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Fusarium Wilt: The One in Your Tomato Bed Cannot Touch Your Beans
Fusarium wilt is locked to its host: UC IPM says the tomato one infects tomatoes only. That changes what you can plant in that bed next year.
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Leaf Miners: By the Time You See the Tunnels, Spraying Is Too Late
The grub is sealed inside the leaf where sprays cannot reach it. Minnesota Extension also says the damage barely matters — unless the leaf is the part you eat.
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Septoria Leaf Spot: The Tell Is Inside the Spot
Septoria leaf spot: many small spots with pale centers and tiny black specks inside. Those specks separate it from early blight and decide what you do next.
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Downy Mildew: The Straight-Edged Patches Are a Cucumber Thing
Downy mildew’s angular, vein-bounded spots are cucumber’s tell. NC State says they’re less reliable on melons, and basil downy mildew is another genus.
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Spider Mites: Why the Spray Often Makes It Worse
Spider mites are too small to see, so you diagnose the leaf. Three extension services say common sprays can cause outbreaks. Here’s what to do instead.
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Tomato Blight: One Name, Two Diseases, and Opposite Instructions
Tomato blight is two diseases. Early blight you manage over a season. Late blight blows in and kills in days. Telling them apart decides what you do today.
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Tomato Hornworm: How to Find It, and the One You Must Not Kill
Find hornworms by their droppings, not by hunting green on green. And if yours is covered in white cocoons, leave it — it's already dead and working for you.
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Tomato Leaves Curling: Which Way They Roll Tells You Whether Anything Is Wrong
Tomato leaves curling upward from the bottom is physiological leaf roll, which UC IPM says won’t harm the plant. Curling downward with twisted growth is not.
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Tomato Leaves Turning Yellow: How to Tell Which Cause It Is
Yellow tomato leaves have five common causes and the yellow alone can't tell them apart. Use the spots, the pattern, and which leaves are hit — extension-sourced.
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Squash Bugs: Why Spraying the Ones You Can See Does Not Work
Squash bugs: by the time you see adults, spray is your weakest tool. The fight is eggs and fresh nymphs. Here’s the timing, from extension sources.
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