Major Diseases |
Caused By |
Symptoms |
Control |
Fungal Disease |
|
|
|
Bottom rot |
Rhizoctonia solani |
Usually wilting of the outer leaves |
Provide good drainage and weed control |
Grey mold |
Botrytis cinerea |
Water soaked, then grayish green or brown, and finally turn into a brownish-gray, slimy mass. |
-keep the humidity low and the temperature warmand sterilize soil before planting
-Keeping the plants as dry as possible helps prevent infection, so avoid overhead watering |
Downy mildew |
Bremia lactucae |
-Symptoms appear first on oldest leaves. -Yellowish or light green blotchy areas appear on the upper sides of leaves |
Use resistant varieties |
Fusarium wilt |
Fusarium oxysporum |
-The first symptoms may occur in seedlings that wilt and die. -Mature plants have a characteristic red-brown streak. |
Effective control measure is to avoid planting head lettuce in infested fields for at least several years |
Leaf drop |
Sclerotinia minorĀ & Sclerotinia sclerotiorum |
First symptom that is noticed is wilting of the outermost leaves |
-Use long rotations away from lettuce, beans, celery, or carrots
-Well- drained soil and/or use raised beds |
Powdery mildew |
Erysiphe cichoracearum |
-Covered by the fungal hyphae, giving it a powdery or dusty appearance |
-Can be managed if tolerant varieties of lettuce are available |
Viral Disease |
|
|
|
Alfalfa mosaic |
Alfalfa mosaic virus |
|
Cultural and biological practices |
Lettuce mosaic |
Lettuce mosaic virus |
plants are often irregularly shaped and mottled yellow and green |
Use certified disease-free seed |
Cucumber mosaic |
Cucumber mosaic virus |
|
|
Beet western yellows |
Beet western yellows virus |
|
|
Lettuce infectious yellows |
Lettuce infectious yellows virus |
Plants are stunted with overall yellowing and leaf margins of older leaves may turn brown |
Control weed hosts |
Big vein |
Virus-like agent |
A pronounced clearing of the chlorophyll next to major veins |
Disease can be controlled by planting tolerant varieties and avoiding fields with known history of disease |
Abiotic disease |
|
|
|
Tip burn |
Calcium deficiency or excessive nutrients or warm temperature or enhanced light |
Symptoms are dark brown spots near the leaf margin followed by marginal necrosis of leaves |
Ca application |
Nematode disease |
Nematode |
|
Crop rotation, cultural practices |