Fungal Diseases and Insect Pests: What to Watch For

The Basics Worth Knowing

Most plant disease and pest problems follow patterns. Once you understand a few of those patterns, you stop reacting to every brown spot and start making better decisions about what actually needs intervention.

This guide focuses on the fungal diseases and insect pests most relevant to berry growers, fruit tree growers, and edible-plant gardeners — the kinds of plants we grow and sell. It is not an encyclopedia. The goal is to help you recognize the problems that matter most, understand the conditions that drive them, and think through prevention before reaching for a spray bottle.

Fungal Diseases

Fungal diseases are the most common category of plant disease in edible crops. They thrive when moisture sits on plant tissue for extended periods, when air circulation is poor, and when susceptible varieties are planted without attention to site conditions.

A few things worth understanding upfront:

• Fungi spread through spores. Spores need moisture (usually free water on leaf or fruit surfaces) to germinate and infect.
• Most fungal infections happen during specific weather windows — warm and wet, cool and damp, or humid with poor air movement, depending on the pathogen.
• Prevention matters more than cure. Once a fungal infection is established in plant tissue, you cannot reverse the damage to that tissue. You can only protect new growth and reduce further spread.
• Sanitation is not glamorous, but it is the single most cost-effective disease management practice. Removing infected plant material reduces the reservoir of spores available for future infection.

Anthracnose

Anthracnose is one of the most damaging diseases on caneberries (raspberries, blackberries) and blueberries. On brambles, it appears as small, sunken purple or gray spots on canes, often with a lighter center. As infections advance, the spots enlarge and merge, weakening canes and reducing yield. On blueberry, anthracnose primarily affects ripe or ripening fruit, causing soft, sunken lesions that ruin the harvest.

Anthracnose thrives in wet weather during the growing season. Splashing rain moves spores from old infected tissue onto new growth. Dense plantings with poor air circulation hold moisture longer and make the problem worse.

What helps: prune to improve air movement. Remove and destroy old, infected canes after harvest. Avoid overhead irrigation during fruiting if possible. In production settings, protective fungicide programs (applied before symptoms appear) are standard practice — consult your local extension recommendations for timing specific to your region.

Botrytis Gray Mold

Gray mold is common across a wide range of crops — berries, strawberries, tomatoes, flowers. You will recognize it by the fuzzy gray-brown sporulation that develops on infected tissue, especially on ripe or damaged fruit. It can also attack flowers, preventing fruit set, and infect wounded cane tissue on brambles.

Conditions that favor botrytis: cool to moderate temperatures with high humidity or prolonged wetness. Dense canopies, fruit sitting in contact with wet soil, and wounded tissue all increase risk.

What helps: harvest ripe fruit promptly. Improve air circulation through the canopy. Avoid working with plants when foliage is wet (you become a spore vector). Remove and discard moldy fruit rather than leaving it in or near the planting. For brambles, adequate cane spacing and thinning are the single most effective cultural practices against gray mold.

Powdery Mildew

Unlike most fungal diseases, powdery mildew does not need free water to infect — high humidity is enough. It appears as a white or grayish powdery coating on leaves, shoot tips, and sometimes fruit. Blackberries are more commonly affected than raspberries. On susceptible varieties, powdery mildew can distort new growth and reduce fruit quality.

Conditions that favor it: moderate temperatures, high humidity, and still air. Shaded or crowded plantings are particularly prone.

What helps: variety selection matters here — some cultivars are significantly more susceptible than others. Adequate spacing, sunlight exposure, and air circulation all reduce powdery mildew pressure. Fungicide applications are most effective when applied preventively before symptoms are widespread.

Phytophthora Root Rot

Phytophthora is a soil-borne water mold (technically not a fungus, but managed similarly) that attacks root systems. It is most damaging in heavy, poorly drained soils and in low-lying areas where water collects. Affected plants show general decline — wilting despite adequate soil moisture, stunted growth, off-color foliage, and eventual death. Blueberries and raspberries are both susceptible.

Phytophthora is driven by waterlogged conditions. Once established in a site, it persists in the soil.

What helps: site selection is critical. Plant in well-drained soil, use raised beds where drainage is marginal, and avoid planting in areas with a history of root rot. Resistant rootstocks or varieties can reduce risk where available. Phosphonate-based treatments (FRAC group P07) are used in production settings to suppress phytophthora, but they are not a substitute for correcting drainage problems.

Mummy Berry

Mummy berry is primarily a blueberry disease. It has a distinctive two-phase cycle: in spring, the fungus produces structures from fallen, mummified fruit on the ground. These release spores that infect new shoots, causing them to wilt and brown (the "shoot strike" phase). Later, a second spore type infects flowers and developing fruit, causing the berries to shrivel and drop as hard, gray "mummies."

Conditions that favor it: moist spring weather during bloom and early growth. The mummies on the ground from the previous year are the primary source.

What helps: rake or remove mummies from under bushes before spring. A fresh layer of mulch can bury remaining mummies and reduce spore release. In production, fungicide applications are timed to the shoot-strike and bloom phases — specific timing depends on your climate and weather patterns each spring.

Other Diseases Worth Recognizing

• Spur blight on raspberries: brownish-purple lesions at the base of leaf stalks on first-year canes, weakening fruiting spurs. Favored by wet weather and dense growth. Thin canes and improve air circulation.
• Cane blight: enters through wounds (pruning cuts, insect damage, mechanical injury) and kills canes. Keep tools clean, make clean pruning cuts, and avoid working in wet conditions.
• Orange rust on blackberries: bright orange spore masses on leaf undersides in spring. Systemically infects the plant — dig and destroy infected plants entirely, as they cannot be cured.
• Septoria leaf spot on blueberries: small spots with gray centers and dark borders on leaves. Primarily causes premature leaf drop. Improve air circulation and remove fallen leaf litter.

Insect Pests

For outdoor berry and fruit plantings, the insect pest picture is quite different from indoor growing. Outdoors, you have natural predators, weather events, and far more environmental variability working in your favor. The pest pressure tends to be seasonal rather than chronic.

Spotted Wing Drosophila (SWD)

SWD is arguably the most economically damaging insect pest for berry growers in the eastern US. Unlike common fruit flies that only infest overripe or damaged fruit, SWD females cut into intact, ripening fruit and lay eggs inside. The larvae feed within the fruit, causing collapse, softening, and secondary rot.

SWD is active during the fruiting season, especially in moderate temperatures. Populations build throughout the summer and are often worst on later-ripening varieties.

What helps: harvest frequently and thoroughly — don't leave ripe fruit on the plant. Refrigerate harvested fruit promptly (cold slows larval development). Remove and destroy dropped or unmarketable fruit. Monitoring traps can help detect the presence and timing of SWD activity. For growers who use insecticides, spray timing relative to the ripening window is critical, and pre-harvest intervals must be respected.

Japanese Beetles

Japanese beetles feed on foliage of many fruit crops, particularly caneberries, grapes, and some tree fruits. The damage is distinctive: skeletonized leaves where the beetles consume tissue between the veins, leaving a lace-like pattern. Heavy feeding reduces the plant's ability to photosynthesize and can weaken fruiting.

The adults are active mid-summer. Grubs (larvae) develop in turf soil from late summer into the following spring.

What helps: handpicking is effective for small plantings — beetles drop readily when disturbed, especially in morning when they are less active. Japanese beetle traps are controversial; they can attract more beetles than they catch. For larger plantings, targeted insecticide applications may be warranted during peak adult activity. Grub control in surrounding turf (milky spore, beneficial nematodes) can reduce local populations over time.

Spider Mites

Spider mites affect both indoor and outdoor plantings. Outdoors, they tend to flare during hot, dry weather when natural predator populations are disrupted (often by broad-spectrum insecticide applications that kill predators along with target pests). Two-spotted spider mites are the most common species on berries and many edibles.

For detailed identification and management of spider mites, see our guide on Common Pests on Indoor Fruit Plants — the biology and management approach is similar whether plants are indoors or out.

Scale, Aphids, and Other Sap Feeders

Various scale insects, aphids, and other sap-feeding insects can affect fruit crops. Aphids are usually more of a nuisance than a crisis outdoors, since predator populations (ladybugs, lacewings, parasitic wasps) generally keep them in check. Scale insects tend to be more persistent and harder to notice until populations are established.

What helps: encourage natural predators by avoiding unnecessary broad-spectrum insecticide applications. Monitor for scale on woody stems during dormancy when they are easier to spot. Dormant oil applications in late winter can reduce overwintering scale and mite populations effectively.

Prevention: The Short List

If you remember nothing else from this guide, these practices cover the most ground:

• Site selection and drainage: many root diseases are effectively prevented by planting in well-drained soil. You cannot spray your way out of a waterlogged site.
• Air circulation: prune to open up the canopy. Adequate plant spacing pays for itself in reduced disease pressure year after year.
• Sanitation: remove infected plant material. Rake up fallen fruit and leaves. Clean pruning tools between plants when working with disease-prone crops.
• Harvest discipline: pick fruit when ripe. Don't leave it hanging. This is your best defense against fruit-attacking insects and botrytis.
• Monitor before you spray: know what you're dealing with before you act. Many garden problems resolve without intervention, and spraying the wrong thing at the wrong time wastes money and can make things worse.
• Start with healthy plants: tissue-cultured and pathogen-indexed planting stock eliminates many systemic disease problems before they start. This is especially relevant for caneberries, where viruses and systemic pathogens can be propagated along with the plant itself.

When Chemical Controls Enter the Picture

Fungicides and insecticides are legitimate tools when used thoughtfully as part of an integrated approach. But they are not the first line of defense, and they are not a substitute for the cultural practices above.

A few principles that experienced growers consistently follow:

• Preventive timing beats reactive spraying. Most fungicides work by protecting healthy tissue from new infections — they do not cure tissue that is already infected. Applying after symptoms are widespread is usually too late for that infection cycle.
• Rotate modes of action. Fungi can develop resistance to fungicides when the same chemistry is used repeatedly. FRAC (Fungicide Resistance Action Committee) groups classify fungicides by their mode of action. Rotating between different FRAC groups helps preserve the effectiveness of the tools you have.
• Read the label. The product label is the legal document that governs what you can apply, to which crops, at what rate, with what pre-harvest interval, and under what conditions. This is not a suggestion — it is a legal requirement, and it exists to protect both the grower and the consumer.
• More product is not better. Applying above the labeled rate does not increase effectiveness and can cause plant injury, environmental contamination, or illegal residues.

Our companion guide, Understanding Crop-Protection Products, goes deeper into active ingredient categories, FRAC groups, and how to think about product selection responsibly.