Green beans are productive and easy to grow, but several insects, diseases, and environmental conditions can reduce plant health and yield. It is important to address these issues as soon as they are observed.
Mexican Bean Beetle | Aphids, Leafhoppers, and Fleahoppers | Spider Mites | Bean Leaf Beetle & Corn Earworm | Leafminers | Bacterial Blights, Brown Spot, & Halo Blight | Anthracnose | Bean Rust | Alternaria Leaf Spot | Viral Diseases | Poor Emergence | Flower Drop & Poor Pod Set | Decline in Productivity | Large or Seedy Pods | More Information
Insect Pests
Mexican Bean Beetle
Symptoms: Adults and larvae feed on the undersides of leaves, creating a lacy or skeletonized appearance. Severe feeding reduces photosynthesis and weakens plants.
Management: Scout regularly for yellow egg masses and larvae and remove them by hand. Use row covers to exclude beetles. Clean up plant debris to reduce overwintering populations. In severe cases, insecticidal soaps, neem, or spinosad may be used.
Aphids, Leafhoppers, and Fleahoppers
Symptoms: These sap-feeding insects cause curling, yellowing, or distorted leaves and can transmit viruses. Leaves may appear sticky due to honeydew.
Management: Encourage natural predators, spray strong water streams to dislodge insects, or use insecticidal soap. Avoid excess nitrogen that promotes tender growth.
Spider Mites
Symptoms: Fine speckling, yellowing, and eventual bronzing of leaves, often during hot, dry weather. Severe infestations cause leaf drop.
Management: Maintain adequate moisture and reduce plant stress. Wash foliage with water and apply insecticidal soap if needed.
Bean Leaf Beetle and Corn Earworm
Symptoms: Bean leaf beetles chew holes in leaves and may damage pods. Corn earworm larvae feed on pods, reducing quality.
Management: Hand-pick beetles when feasible. Use row covers early in the season and remove weeds that harbor pests.
Leafminers
Symptoms: Tunnels or winding trails within leaves caused by larvae feeding between leaf surfaces. Severe damage reduces photosynthesis.
Management: Remove and destroy infested leaves. Maintain plant vigor to tolerate minor damage.
Diseases
Bacterial Blights, Brown Spot, and Halo Blight
Symptoms: Water-soaked spots on leaves that turn brown, often with yellow halos. Pods may show lesions and become misshapen.
Management: Control of bacterial diseases focuses on prevention. Use disease-free seed and resistant varieties. Avoid overhead watering and working in wet plants. Rotate crops and remove plant debris.
Anthracnose
Symptoms: Dark, sunken lesions on pods, stems, and leaves. Seedlings may be girdled and die.
Management: Plant certified disease-free seed. Rotate crops for several years and remove infected plants promptly.
Bean Rust
Symptoms: Small reddish-brown pustules on leaves that lead to yellowing and premature leaf drop.
Management: Select resistant varieties and practice crop rotation. Remove plant debris and improve air circulation.
Alternaria Leaf & Pod Spot
Symptoms: Small dark spots on leaves and pods that enlarge into irregular lesions. Severe infections cause leaf drop.
Management: Promote good air flow with proper spacing. Remove infected foliage and avoid prolonged leaf wetness.
Viral Diseases
Symptoms: Mottled, curled, or distorted leaves and reduced plant growth. Yields are often reduced.
Management: Use resistant varieties and control insect vectors such as aphids. Remove infected plants promptly.
Environmental and Cultural Problems
Poor Emergence
Symptoms: Seeds fail to germinate, or seedlings emerge unevenly or die shortly after emergence.
Management: Plant when soils are warm and well-drained. Avoid planting too deeply and use high-quality seed. Cold, wet soils commonly lead to poor stands. Planting later in the season avoids many of these issues. Seeds can be sown as late as early July for harvest before the frist frost.
Flower Drop and Poor Pod Set
Symptoms: Flowers fall off before pods develop, resulting in low yields.
Management: Maintain consistent soil moisture and avoid stress. High temperatures, especially above 90°F, and drought are common causes.
Decline in Productivity
Symptoms: Plants produce fewer or smaller pods over time. Growth may appear weak.
Management: Ensure full sun, consistent watering, and balanced fertility. Avoid excess nitrogen, rotate crops, and manage pests and diseases to maintain vigor. Harvest plants often as pods allowed to fully mature will prevent new pods from forming.
Large or Seedy Pods
Symptoms: Pods become oversized, tough, or fibrous with large seeds.
Management: Green beans are harvested when the pods are immature. If left on the plant too long, pods will mature and be less palatable. Harvest beans frequently while pods are young and tender to maintain quality and encourage continued production.
More Information
- All About Beans
- Growing and Caring for Your Vegetable Garden: Insect Pests
- Managing Diseases in the Vegetable Garden
- Weather-Related Problems in the Vegetable Garden
- Weed Management in the Home Garden
- Suggested Vegetable Varieties for the Home Garden
- Crop Rotation in the Vegetable Garden
Photo credits: 1: Howard F. Schwartz, Colorado State University, Bugwood.org; 2: Ansel Oommen, Bugwood.org; 3: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org; 4: Howard F. Schwartz, Colorado State University, Bugwood.org; 5: Howard F. Schwartz, Colorado State University, Bugwood.org; 6: Thirunarayanan Perumal, Banaras Hindu University, Bugwood.org; 7: Howard F. Schwartz, Colorado State University, Bugwood.org