Blueberry plants affected by leaf spot diseases results in quite a bit of damage annually. It's important to control leaf spot diseases by watching closely for symptoms and controlling the disease with fungicide and regular pruning. Keeping an eye out for insects is also important. There are many ways to control pests, such as insecticides and biological methods.
There are a variety of leaf spot diseases that affect blueberry plants. Gloeosporium leaf spot is one of the most common. Check for symptoms of the disease, which are flecking, stem lesions and leaf anthracnose, which is a general term used often for fungal diseases that cause lesions on plants.
Septoria leaf spot tends to affect cultivated highbush and rabbiteye blueberry, according to W.O. Cline, extension plant pathologist at North Carolina State University. Look for leaf spots with white or tan centres and purple borders. To manage leaf spot diseases, plant blueberry cultivars that are resistant to leaf spot and limit overhead irrigation.
Controlling leaf spot diseases requires fungicides, consistent pruning throughout the summer months and resistance, which means planting types of blueberry plants that are able to fight off disease. This varies with soil, weather and geography. Resistance is only partly effective anyway so fungicides will most likely be needed. Apply the fungicide as early as possible to control the disease. It's a good idea to make at least one application before harvest on some plants, such as highbush and rabbiteye. Future applications should be 2 weeks apart from harvesting to mid-August. Don't use crop oils early in the season, as this increases the chance of leaf spot diseases, according to Cline. Regular pruning also helps control leaf spot by getting rid of older, infected leaves.
Several insects can prove problematic for blueberry plants. Leafrollers aren't usually an issue unless there are more than 15 on a plant. Leafhoppers, which are often found underneath leaves, may transmit blueberry stunt mycoplasma, which will affect production. Aphids are a concern with young plants, as they can cause sap loss. Avoid insecticides, because most aphid infestations are controlled by natural enemies and any insecticides will kill both; this could give aphids an edge. Because aphids can also cause blueberry shoestring virus, remove all plants with bright red streaks.
There are several ways to ensure blueberry plants are safe from invasion. Biological control, such as allowing ladybird beetles to feed on aphids, will work in many cases.
You can also try a more mechanical method of control, such as hand removing pests or even simply spraying plants with a garden hose. Choosing cultivars that are resistant to pests will also help with control issues.
For pesticides, Sevin and malathion are the two usually used. For leafroller larvae and blueberry maggots, try malathion. It can also help with aphids if the infestation becomes too great to reply on biological methods. Sevin will work on leafrollers but not aphids. Never use Sevin when plants are in bloom.
If you're having trouble growing blueberry plants, consider your soil, climate and how old the plant is. Blueberries need very acidic soil that contains plenty of moisture for best growth. You can do a pH test on soil to determine its acidity. Adding proper amounts of sulphur and fertiliser can help prepare soil.
As far as climate, blueberries normally don't do well when temperatures dip below -6.67 degrees C. Keep in mind that it takes these plants up to 6 years to become fully productive and they need full sun.