Fusarium Crown Rot
Beginner
Scientific Names
Fusarium oxysporum f.sp. asparagi, Fusarium proliferatum, Fusarium verticillioides
Identification
- Crown rots caused by Fusarium cause yield decline and can limit the productive life of an asparagus planting.
- Infected roots turn brown and mushy, limiting the plant's ability to move water and nutrients into the fern.
- Plants become stunted, turn yellow and lose their foliage (cladophyls).
- Over time, the infected plants die leaving large gaps in the plant stand.
- Reddish-brown, oval-shaped lesions may be visible on the root surface and lower stems (just below the soil line).
- Infections may predispose the spears to post-harvest decay.
Often Confused With
Phytophthora
Period of Activity
Infections may occur at any time in the crop cycle. F. oxysporum persists in the soil for long periods of time. Fusarium proliferatum and Fusarium verticillioides are less persistent; they are usually associated with infested crop residue.
Over time, all asparagus fields will develop fusarium.
Scouting Notes
Take note of any yellowing or undersized plants while scouting. If fusarium is suspected, dig up a section of the crown and look for vascular discolouration. Document the location of the damage and the percentage of plants affected.
Thresholds
None established.
Advanced
Scientific Names
Fusarium oxysporum f.sp. asparagi, Fusarium proliferatum, Fusarium verticillioides
Identification
Crown rot causes yield decline and can limit the productive life of an asparagus planting. Infected fields have poor stands with many gaps within the rows. Reddish-brown lesions may be present at the base of the stem, just below the soil surface.
Symptoms on the fern include stunting and bright yellow foliage on one or more stalks per crown. Infected crowns typically produce fewer stalks per crown than their uninfected neighbours.
Infected stems and roots may have a brown discolouration of the vascular tissue. The centre of diseased roots turns reddish-brown and may develop a dry-rot. Severely infected crown tissue may become completely hollow.
Often Confused With
Phytophthora
Biology
Fusarium are soil-borne fungi. F. oxysporum f.sp. asparagi is host specific to asparagus. It persists in the soil as chlamydospores. Fusarium proliferatum and Fusarium verticillioides do not produce chlamydospores. They survive in residue as microconidia.
New infections enter a field from infected seed, infected crowns or even wind-borne soil particles. Concentrations in the soil increase over time as more plants become infected.
Fusarium species colonize roots and crowns, invading directly through root tips or through wounds caused by tillage implements, cutting tools, or below-ground insect feeding. Infection may also occur above-ground through wounds on the stem caused by insect damage or sand-blasting. Fusarium may also be spread from plant to plant by insects such as the asparagus miner.
Plants are more susceptible to infection during stressful growing conditions caused by drought, excessive weed competition, over-harvesting or premature defoliation. Causes of premature defoliation include insect feeding, early frost and foliar diseases.
Tillage is very harmful to asparagus roots. Even shallow tillage damages the fine surface roots, providing potential infection sites.
It takes at least 5 years after an asparagus crop has been removed for the fusarium to decrease to “base line” levels, after which there is still a high risk of a faster “rebound” of the population should asparagus be replanted in the same location.
Period of Activity
Infections may occur at any time in the crop cycle. F. oxysporum persists in the soil for long periods of time. Fusarium proliferatum and Fusarium verticillioides are less persistent; they are usually associated with infested crop residue.
Over time, all asparagus fields will develop fusarium.
Scouting Notes
Take note of any yellowing or undersized plants while scouting. If fusarium is suspected, dig up a section of the crown and look for vascular discolouration. Document the location of the damage and the percentage of plants affected.
Thresholds
None established.
Management Notes
- Avoid planting asparagus into fields that have previously grown asparagus. Where new asparagus ground is not available, wait for a minimum of 5 years before replanting to asparagus.
- Avoid planting asparagus where corn has been grown in the previous 3 years.
- Use treated seed.
- Plant only vigorous, healthy crowns and minimize any damage to the crowns during planting.
- Minimize tillage or use zero-tillage practices where possible.
- Vigorously growing asparagus plants are less susceptible to crown rot. Avoid stressful growing conditions caused by over picking, pest pressure, weed competition, soil compaction, drought stress and low fertility.
- Ensure that crowns have been grown in fields that are clean of fusarium.
