Garden and crop questions, answered

Last updated: October 2026

Plain answers to the questions gardeners and growers search for most: what is eating a plant, what a home remedy really does, when a spray is worth using and how long to wait before harvest. Every guide answers its question in the first paragraph, names the pest or problem by its common and scientific name, and cites university extension services, government agencies or peer-reviewed research. Browse by topic below, or start from the Pest and Disease Library.

Plant problems and how-tos

• Do mosquito bits and dunks work on fungus gnats?Do Mosquito Bits and Dunks kill fungus gnats? How Bti works on the larvae, how Bits and Dunks differ on the label, and why gnats can linger after treatment.
• Does dish soap kill aphids without hurting plants?Does dish soap kill aphids, can a dish soap spray damage plants, and how does it differ from insecticidal soap? Plus what works on aphids in the garden instead.
• Does foliar feeding work?Does foliar feeding work? How leaves absorb nutrients, how foliar compares with soil feeding, which nutrients respond, and why calcium sprays fail on tomatoes.
• Does hydrogen peroxide help plants with root rot and fungus gnats?Does hydrogen peroxide cure root rot or kill fungus gnat larvae? What root dip and hydroponic studies found, how it can harm roots, and what works better.
• Early blight vs late blight: how to tell them apartEarly blight vs late blight on tomatoes: how the spots differ, whether tomato blight lives in the soil, and how to treat each disease before it spreads further.
• How do you get rid of spider mites on indoor plants?How to spot spider mites on houseplants, why dry indoor air lets them multiply, and which natural options, from rinsing to soap and oil sprays, get rid of them.
• How do you stop powdery mildew on squash and zucchini?Powdery mildew on squash, zucchini, cucumber and pumpkin leaves: how to spot it early, which organic sprays work, and why resistant varieties matter most.
• How do you tell jumping worms from earthworms?How to spot jumping worms by the clitellum band, movement and coffee-ground soil, how they differ from European earthworms, and what Asian jumping worms are.
• Neem oil vs insecticidal soapNeem oil vs insecticidal soap: which works better on aphids and spider mites, which one also controls powdery mildew, and how copper fungicide compares.
• Sulfur vs copper fungicideSulfur vs copper fungicide: which one works on powdery mildew, which one suits tomato blights and bacterial spot, and how heat, oil sprays and soil limit each.
• What are biostimulants?What plant biostimulants are, the main types used in farming from seaweed to microbes, how they differ from fertilizer, and what field trials show they deliver.
• What causes brown spots on plant leaves?What causes brown spots on leaves: fungal and bacterial leaf spots versus sun, cold and salt damage, with answers for tomato, indoor plant and apple leaves.
• What do white spots on plant leaves mean?What white spots on leaves mean: powdery mildew, spider mites, thrips or hard water, plus what causes white spots on tomato, squash and indoor plant leaves.
• What is integrated pest management?What integrated pest management (IPM) is, the four steps of an IPM program, how action thresholds work, and which tactics growers combine to slow resistance.
• What organic fungicides work on tomatoes?Organic fungicides for tomatoes: which work on early blight, Septoria, late blight and powdery mildew, how copper and Bacillus compare, and when to spray them.
• Why are my plant leaves turning yellow?Why plant leaves turn yellow: overwatering, light and nutrient causes, plus why leaves yellow in winter, turn yellow and brown, or yellow after repotting.
• Why are my tomato leaves curling?Why tomato leaves curl up or roll inward, how to tell heat and water stress from herbicide drift, leaf curl virus and mites, and what to do about each one.
• Why are my tomato leaves turning yellow?Why tomato leaves turn yellow at the bottom or yellow with brown spots, how to tell early blight, Septoria, wilt and nutrient shortage apart, and what to do.