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While usually an easy plant to grow in rock gardens and hot, dry areas, agave can be susceptible to bacterial and fungal rots if exposed to too much moisture and humidity. Cool, wet spring weather that rapidly changes to hot, humid summer can cause a surge in fungal growth and pest populations. Mid- to late-summer crown rot of agave plants can be common in cooler climates and potted plants. Read on to learn what you can do for agave plants with crown rot.
Agave plants are popular ornamental plants in arid regions around the world. With their striking forms and ability to thrive in hot dry conditions, it’s no wonder they are a mainstay of xeric landscaping. However agaves are susceptible to a number of diseases that can quickly take your prized plants from prime to pathetic. Read on to learn how to identify and treat the most common agave plant diseases.
Common Agave Plant Diseases
Here are some of the most prevalent diseases affecting agaves:
Anthracnose
This fungal disease causes irregularly-shaped brown or black lesions on leaves and crowns. During wet weather, orange fungal spore masses may be visible in the lesions. It spreads via splashing water and wind-driven rain.
Crown and Root Rot
Crown and root rots have various causes, including the fungi Fusarium and Phytophthora. Plants collapse and rot at the base. Roots turn dark and mushy.
Bacterial Soft Rot
Caused by the bacterium Erwinia cacticida, soft rot starts as a soft, water-soaked spot that turns mushy and brown or black. Infected tissue oozes dark liquid and emits a foul odor.
Fungal Leaf Spot
Circular or irregular leaf spots in various colors are caused by different fungal pathogens like Phyllosticta Severe infections cause extensive leaf damage and dieback
Virus Diseases
Viruses like agave mosaic virus cause mottling, streaking, and distortion of leaves. Plants become stunted and decline in health over time.
Freeze Damage
Prolonged below-freezing temperatures cause leaf tips and margins to blacken and die back. Damage ranges from cosmetic to severe dieback depending on duration of cold.
Identifying Agave Diseases
Carefully examine plants to detect problems early before they intensify. Warning signs include:
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Circular or odd-shaped spots on leaves.
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Leaf tips turning brown or black.
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Mushy, discolored roots.
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Foul odor from base of plant.
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Collapsed, rotting lower leaves and crown.
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Distorted growth and mottled leaves.
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Wilting, stunted growth.
Treating Diseased Agave Plants
Once you’ve diagnosed the problem, take action to treat, control spread, and prevent recurrence:
Remove Infected Parts
Prune out all diseased tissue, disinfecting tools between cuts. Seal in bags and discard to prevent spread.
Improve Air Circulation
Space plants appropriately to allow air movement and rapid drying after rain or watering.
Apply Fungicides
Spray leaves thoroughly with appropriate fungicides like thiophanate-methyl. Repeat applications as directed.
Adjust Watering
Allow soil to dry between waterings. Avoid overhead irrigation. Water at base of plants.
Disinfect Tools
Clean and disinfect pruners, shovels, etc. after working with infected plants.
Remove Plants
Severely infected, dying plants should be completely removed and destroyed.
Plant in Well-Draining Soil
Good drainage discourages root and crown rots. Amend clay soils with sand; add organic matter to sandy soils.
Control Insect Vectors
Insects can spread bacterial and viral diseases. Use insecticidal soaps, horticultural oils, and other insecticides.
Improve Air Flow
Allow adequate space between plants for good air movement.
Apply Preventive Fungicides
Where anthracnose, leaf spot, or crown/root rots are common, make preventive fungicide applications.
Preventing Agave Diseases
Prevention is the best medicine when it comes to agave diseases. Follow these tips to maintain plant health:
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Select disease-resistant varieties.
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Give plants sufficient spacing and air circulation.
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Avoid overhead watering.
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Allow soil to dry between irrigations.
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Provide good drainage.
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Disinfect tools after use on diseased plants.
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Scout regularly for early symptom detection.
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Remove diseased plant debris promptly.
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Control insect pests.
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Make preventive fungicide applications where warranted.
While agaves are adapted to warm climates, they aren’t immune to disease. Stay vigilant for early warning signs and be prepared to take action at first notice of infection. Remove infected plants or parts before diseases spread. Follow sound cultural practices to keep your agaves healthy and enhance disease resistance. With prompt identification and treatment, your agaves can continue gracing your landscape for years to come.
How to Save Plants with Crown Rot
It is important to regularly inspect your agave plant for signs of insect chewing and rot, especially if it not growing in optimal conditions. If caught early enough, fungal and bacterial rots can be controlled with selective pruning and treatment of fungicides such as thiophanate methyl or neem oil.
Leaves with chew marks or lesions should be cut off at the crown and disposed of immediately. When pruning away diseased plant tissues, it’s recommended that you dip pruners in a mixture of bleach and water between each cut.
What is Agave Crown Rot?
Agave, or century plant, is native to the deserts of Mexico and hardy in zones 8 to 10. In landscaping, they can be a stunning addition to rock gardens and other xeriscaping projects. The best way to prevent root and crown rot of agave plants is to situate them in a location with excellent drainage, infrequent irrigation, and full sun.
Agave plants should also never be watered overhead, a slow trickle of water right at the root zone can prevent the splashing and spread of fungal spores, as well as prevent the crown rot that can happen if water pools up in the crown of agave plants. Pumice, crushed stone, or sand can be added to the soil when planting an agave to provide more drainage. Container-grown agave will do best in a cactus or succulent soil mixture.
Crown rot of agave may present itself as gray or mottled lesions or, in extreme cases, the plants leaves may entirely turn gray or black and shrivel right where they grow out from the crown. Red/orange fungal spores may also be obvious near the plant crown.
Crown and root rots in agave can also be caused by an insect called the agave snout weevil, which injects bacteria into the plant as it chews on its leaves. The bacteria cause soft, squishy lesions in the plant where the pest then lays its eggs. Once hatched, the weevil larvae tunnel their way to the roots and soil, spreading rot as they work their way throughout the plant.
Plant Diseases and Disorders – Julie Beale
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