5 Plant Diseases to Look For in the Early Spring Garden

Spring rains may bring summer flowers, but too much moisture and cool temperatures can become a breeding ground for pathogenic fungi and disease-causing bacteria. The early-season garden is especially prone to plant diseases when young plants are attacked by pests, spaced too close together, or exposed to excess moisture.

Luckily, you can prevent most plant diseases with organic methods that won’t harm you or your crops. Let’s dig into the five most common spring plant diseases, including how to identify, treat, and prevent them.

5 Most Common Spring Plant Diseases

Pathogens are the “bad guy” bacteria, fungi, and protozoa that cause plant diseases in the garden. It’s important not to confuse them with “good guy” microorganisms that can actually defend our crops from attack. Preventative measures and organic treatments are widely available for most of these issues, ensuring you can preserve the health of your crops and the ecosystem in your garden.

Damping Off (Seedlings)

The most common disease you’ll find in your spring garden only affects seedlings, so if your plants are already past this stage, then you are in the clear! 

Identify

Damping off is most obvious when you see collapsed seedlings that are “girdled” or weakened at the base. In excessively humid or crowded conditions inside a greenhouse or seed-starting area, pathogenic fungi or mold attack baby plants right at the soil level, causing the stems to rot. 

You may also notice:

• Poor germination
• Rotten seeds
• Weakened stems
• Rotted brown stems
• Fluffy, moldy growth at the plant base
• Whole plant collapse

Prevent

The best way to prevent rotten seedlings from damping off is to keep your seed-starting area aerated. This begins with well-drained soil that has lots of air pockets for young roots to breathe. Compost, perlite, and peat moss are great drainage-enhancing materials. Avoid using outdoor garden soil that is heavy or potentially contaminated. Prioritize fresh sowing medium every time you start seeds.

Next, sanitize your trays or pots before sowing. A diluted solution of a capful of bleach in a quart of water can be mixed in a spray bottle and applied to your supplies. 

Once seeds are planted, the most important means of prevention is airflow. Properly thin seedlings and space them according to crop directions so that oxygen can easily flow between the stems and leaves. Add a fan or open a window to bring a breeze into the area. Oxygenation is the key to preventing damping off.

Botrytis (Gray Mold)

Gray mold (caused by Botrytis cinerea) is a common fungal disease that looks exactly as it sounds. Fuzzy, gray-hued mold may grow on dying plant material and spread to live flowers, fruits, and leaves. It is particularly problematic in the wet conditions of spring, but there are plenty of treatments and resistant cultivars.

Identify

Fluffy gray mold and mushy, decayed plant parts are sure signs of botrytis. You may also notice:

• Water-soaked spots on leaves
• White or off-white spots that turn brown
• Wilted leaves
• Grayish or bumpy spore patches
• Hanging rotten fruit

The pathogen overwinters on plant parts or in the soil, then spreads via splashing raindrops or irrigation. It most commonly affects fruit, but at this time of year, it can also attack other plant parts. The disease only thrives and spreads in humid conditions and cool temperatures between 59 and 73°F (15-23°C). Once the summer warms up, you won’t have to worry about it anymore.

Prevent

The best way to prevent botrytis is to encourage airflow and adequate space for crops to breathe. When things are placed too close together, humid air gets trapped and creates a breeding ground for mold. Prune regularly, widen plant spacing, and choose resistant cultivars.

For extremely wet and humid weather, liquid copper can be applied preemptively to flowering and fruiting plants to prevent infection. To inoculate with beneficial, disease-fighting microbes, try beneficial bacteria sprays or soil applications containing Trichoderma and Cladosporium.

Powdery Mildew

Another mold-like spring plant disease is powdery mildew. This one is distinct from botrytis because the spores appear more white, like baking flour dusted over your plants. Powdery mildew can also thrive in a wider range of weather conditions, often persisting into the heat of summer.

Identify

Plants that look like they’ve been covered with white dust almost always have powdery mildew. The powdery spots or patches can cover the upper and lower surfaces all over the plant. The key exceptions are unique varieties of summer squash or cucumbers that naturally have white veining on their leaves. 

You may also see:

• Cupped, twisted, or deformed foliage
• Yellow or brown infected leaves
• Stunted, slow growth
• Infected flowers and fruit
• Fallen or dead infected foliage

Prevent

Like most of the fungal diseases we’ve discussed so far, aeration is the best prevention. Pruning, wide spacing, and air flow ensure that air doesn’t become stagnant between your crops. Water gently at the base of the plant to keep powdery mildew spores in the soil, rather than on foliage.

Early Blight

In contrast to late blight, early blight attacks Solanaceae family crops in the early spring. This blight has a preference for tomatoes, potatoes, and peppers. Fortunately, early blight is far more deadly than late blight, and you have plenty of time to save your crops. 

Identify

Lower leaves are the first to show symptoms, including yellowing, brown spots or lesions, and a burnt appearance on the foliage. The pathogen overwinters in the soil and spreads in moist conditions, especially once the spring weather starts warming over 70°F (21°C). 

Tomatoes are the most common victims and will show signature “bullseye” marks with brown centers and yellow outsides. The spots can appear on leaves and stems, traveling upward from the soil level. 

Prevent

Mulching is a great strategy for preventing overwintered spores from migrating up to your crops. Early blight can live in the soil and wait for the right conditions to spread. Mulch prevents water from splashing upward and infecting leaves.

Tomato pruning and suckering are also key strategies. Too much cluttered foliage invites early blight spores to spread rapidly among and within individual plants. Widen spacing in humid climates, especially if you’ve dealt with this disease before. Plant blight-resistant cultivars for maximum defense. 

Downy Mildew

Humid climate gardeners are likely already familiar with downy mildew. This mildew is distinctive from powdery mildew because it only forms on the undersides of leaves and does not cause the powder-like appearance of powdery mildew. It is caused by a water mold (oomycete microbe) that thrives in wet conditions on plant leaves. 

Identify

Downy mildew begins as little white or purplish-gray speckles on the underside of leaves. AS it spreads, the upper leaves develop yellow spots and a fuzzy coating. The pathogen spreads very rapidly in humid conditions and can quickly cause widespread yellowing, stunting, and leaf drop.