Cultural Practices to minimize Disease and Insect problems in Asparagus
1. ] Purchase vigorous, healthy crowns from a reputable supplier. Asparagus, being susceptible to diseases, viruses and insects, some varieties have been bred or hybridized to be resistant to certain pests.Resistance to these pests is usually listed on the plant label using the following abbreviations:
V = Verticillium Wilt
F = Fusarium Wilt
FF = Fusarium Wilt race 1 and 2
N = Nematode
T = Tobacco Mosaic Virus
A = Alternaria (Early Blight)
TSW = Tomato Spotted Wilt
Remember that resistance to these problems does not mean they are 100 % immune, good cultural practices are still important.
2.] Crop Rotation in your garden planting area.
3.] Remove and destroy all plant refuse in the fall and use deep cultivation to bury any remaining refuse.
4.] Do not place diseased plants in the compost heap, as this will only serve to carry bacterial or fungal infestation into the next growing season.
5.] Avoid over watering . Use surface watering methods. Do not handle plants when the vines are wet.
6.] Weeds compete with vegetables for soil moisture and nutrients and also serve as hosts for insects and disease carrying bacteria and fungus. Control weeds in and around the garden .
7.] Control insect pests such as aphids, which are known to transmit diseases from plant to plant.
8.] Use plastic or organic mulches to reduce disease and blossom-end rot problems.
9.] Choose a sunny location . Leaf disease problems are much less likely to occur in a sunny location than in a shady one.
10.] Apply recommended fungicides according to label directions at the first sign of leaf spot diseases
11.] Remove abnormal or unhealthy appearing plants as soon as they are observed. To reduce the spread of suspected diseases wash hands and tools with a mild detergent or alcohol after handling suspect plants.
Asparagus Beetles
Asparagus Beetles are possibly the most serious pest of Asparagus. Adults are a blue/black beetle with a red underside and yellow spots. The larvae are a soft, green /Yellow grub. Both feed on asparagus spears by chewing the tips and spear surfaces which leads to scarring and staining of the spears.
Eggs are laid on developing spears with the eggs being small, elongated and black – sticking out lengthwise from the side of asparagus spears.
Early control of beetles is important in order to to reduce feeding damage later. The first defense once their presence has been detected is Pyrethrin
Do not compact the soil over the newly filled trench or the emergence of the asparagus will be severely reduced. Spears should emerge within one week in moist soils. By mid-season of the planting year, a ridge forms that is 4 inches to 6 inches high and 2 feet wide over the asparagus crowns. Maintain this ridge for the duration of the planting.
Malathion Spray, will provide an effective chemical control in the event of severe chronic infestation .Effective Predator insects are Lady Bugs and Lace wings
Other Common Pests include
Fusarium Root and Crown Rot
The major disease problem of asparagus is caused by two species of fungi. It causes decay of storage roots, stems and crowns. This fungus is present in all agricultural soils and infects corn, grasses, and related plants as well as asparagus.
The fungus colonizes old roots and crowns, invading directly through root tips or through wounds Asparagus plants which are under stress are more susceptible to this infection than those which are growing vigorously.
Affected spears may shrivel and rot in spring before or after emergence Infected crowns have hollow, rotted feeder and storage roots . When crown and stem tissue is sliced open, a reddish-brown discoloration is visible. Symptoms on the fern includes stunting, yellow to brown discoloration of one or more stalks per crown, and fewer stalks per crown . Affected crowns decline in vigor and die.
Fungicide drenches are sometimes used for root and crown rot diseases. No fungicides control all pathogens, most only treat a few. Some fungicides are highly toxic, and residual traces in treated soil can kill plants.
Most Fungicides used against Fusarium include the active ingredient Prothioconazole
Other fungicides registered for use against Fusarium include Fludioxinil and Prochloraz
Fungicides for Fusarium
Asparagus Rust
“Asparagus spears are usually harvested before extensive rust symptoms appear. Symptoms are first noticeable on the growing shoots in early summer as light green, oval lesions, followed by tan blister spots and black, protruding blisters later in the season.
There are three distinct stages of rust disease.
In the first stage, occurring from April to July, lesions develop. These oval lesions are raised, light green in color, and 10-20 mm in length . The lesions are sometimes inconspicuous and decrease in number from the base of the shoots upward. The lesions turn cream-orange in color and become sunken in the center as they mature. During summer months, the second stage of rust disease begins as reddish-brown, blister-like pustules develop on the asparagus shoots.
When the pustules mature, they release large numbers of rust-colored spores that cause new infections throughout the summer. Reddish, rust-colored, powdery spores are seen when rubbed against light-colored clothing. Later in the season the third stage replaces rust-colored spores with black, over-wintering spores. In some lesions, both reddish-brown and black spores appear together. Plants affected by rust are more susceptible to Fusarium crown and root rot.
Spores overwinter on host plant residue, germinate in early spring, and produce new infections on growing asparagus spears. The light green, oval lesions are surrounded by a concentric ring pattern. In young plantings, before stalks are harvested, lesions develop yellow spore-bearing structures in concentric rings.”
Plant Pathology University of Minnesota
There is no tried and true fungicide for Rust that works 100% of the time. Most of the fungicides available are capable of doing as much harm as good. There are some organic remedies which can help.
Baking Soda leaves an alkaline residue on leaf surfaces which inhibits the germination of fungal spores. It prevents and reduces Rust as well as other fungal diseases such as Powdery Mildew.
Adding powdered milk to your Baking Soda is also helpful. Powdered milk will actually enhance your plant’s immune system, it’s a natural germicide. 1/2 cup powdered milk 1/2 cup baking soda in a gallon of water and you have a home made fungicide. See Also: Milk for Powdery Mildew
Another good preventative measure is Neem , if you already have it around for other uses it will help prevent rust and other fungal disease.
2 tablespoons of neem oil in a gallon of water.
You can also add a small amount of neem to the milk baking soda concoction. If you are doing this – I wouldn’t leave any lying around , I did this once and there was a chemical reaction of the 3 ingredients – harmless to plants – but the stench – fahgetaboutit.
Grey Mold
Also known as Botrytis Rot (Botrytis cinerea).
The fungus that causes gray mold invades the plant and flower bracts that have been damaged by slugs ,frost, insects, or other factors. Infected plants turn brown on the outside. On the inner surface is the characteristic gray growth . The fungus survives on decaying organic matter. Botrytis rot is most common during rainy weather. Plant in well-drained areas. Remove infected plant parts and protect plant buds from damage caused by invertebrates. When storing chokes, remove infected chokes immediately.
Any fungicides registered for grey mold control must be applied before infection takes place, they won’t cure an existing infestation. If you’ve had problems with gray mold in the past apply fungicide before the infestation gets to the plant.
Avoid injuring the foliage. Damaged foliage from Fertilizer-burn or frost- is much more susceptible to grey mold infection.
Avoid densely spaced seedlings growing levels by selecting a container that allows adequate spacing for seedling development. Containers can also be placed at a wider spacing to allow better air circulation during periods when seedlings are especially vulnerable.
Follow a strict sanitation policy that includes removal and destruction of all plant debris, prompt removal of infected seedlings, and sterilization of containers ,growing area and surfaces between plants.
Avoid excessive moisture, and allow for proper aeration to reduce the presence of moisture for more time than is actually necessary.
Powdery Mildew
Powdery Mildew “appears as a dusty white to gray coating over leaf surfaces or other plant parts . In most cases this fungal growth can be partially removed by rubbing the leaves. It might be identified incorrectly as dust that has accumulated on the leaves.
Powdery mildew, however, will begin as discrete, usually circular, powdery white spots. As these spots expand they will coalesce, producing a continuous matt of mildew (similar to dirt or dust). A plant pathologist using a microscope can determine whether a fungus is present anytime the whitish patches are present.” Extracted From – Cornell University Powdery Mildew Fact Sheet.
There are a number of products which can be utilized to control and eradicate Powdery Mildew
Related: Are Asparagus Berries Toxic?