The Guava root-knot nematode- A new pest in Louisiana

Charles Overstreet  |  7/16/2018 7:43:02 PM

The guava root-knot nematode (Meloidogyne enterolobii) is considered to be the most damaging root-knot nematode in the world because of its wide host range, aggressiveness, and ability to overcome the resistance that has been developed against root-knot nematodes in many crops. Although this nematode was originally described from the Pacara earpod tree in China, it has been particularly damaging to guava orchards in Brazil. At the present time, it is thought to be very limited in distribution in Louisiana, occurring at only one location. In the likelihood that this nematode begins to spread or get introduced from other states (Florida, North and South Carolina) that have this nematode, our producers and gardeners need to know what to look for and what we know about this nematode.

Figure 1. Bumps, knots, and cracking of a sweetpotato storage root from the guava root-knot nematode. Egg masses of the nematodes visible inside the root on the right.

The guava root-knot nematode is very similar to our common Southern root-knot nematode. On very susceptible plants, expect to see very large galls associated with the roots with the guava nematode. However, the Southern root-knot nematode can produce some rather large galls on very susceptible plants that would make it difficult to distinguish between the two nematode types. Both nematodes can cause severe damage to plants, reducing yields and causing early death. Stunting, yellowing of the foliage and early wilting during drought are also typical symptoms of both nematodes. One of the best ways for producers or gardeners to recognize that the guava nematode is present is when resistant crops to the Southern root-knot nematode get seriously damaged. Crop varieties that have been developed to be resistant to our common root-knot rarely get more than a few small galls and plants do well in the presence of that nematode. If the guava root-knot nematode is present, large galls will be evident on these plants. In the case of sweetpotato, the storage roots are severely deformed, with large cracks and knots on the roots.

Figure 2. A tomato root with root-knot resistance has very little if any galling when in the presence of the Southern root-knot nematode. The susceptible tomato in the same bed was severely galled.

Figure 3. A tomato root severely galled by the guava root-knot nematode (photograph courtesy of Dr. Don Dixon in Florida).


Figure 4. Small bumps and slight cracking from Southern root-knot nematode on sweetpotato. Few egg masses visible under each bump.

If this nematode develops into a problem in Louisiana, crop rotations and use of nematicides will be the primary methods used to manage this pest. Since there are differences reported in crops to this nematode, evaluations will be carried out to identify varieties that may be able to hold up against this pest.There are reports from various scientists about the host status of many plants to the guava root-knot nematode. Many plants are considered to be susceptible and some are considered resistant. Unfortunately, there are some conflicting results with several crops as to whether they are resistant or susceptible. This variability may be related to different populations of the nematode in different areas or differences in varieties. At this point we do not know much about the one that has recently been found in Louisiana except that it is particularly damaging to sweetpotato and tomato.

Table 1. Agronomic or cover crops and their reaction to the guava root-knot nematode

Susceptible crops

Resistant crops

Common vetch

Annual ryegrass

Cotton

Black Oats

Peanut*

Millet

Soybean

Corn

Sugarcane (S-R)**

Oats

Sunn Hemp (S-R)

Radishes

Sweetpotato

Rapeseed

Tobacco

Rice

Rye

Sorghum

Sunn Hemp (S-R)

Velvet bean

Wheat

*Peanut supports develop of females not eggs and is considered potential host in future.

**Crop has been reported susceptible or resistant and the reaction is likely due to different populations of the nematode or different varieties.


Table 2. Vegetable crops and their reaction to the guava root-knot nematode

Susceptible crops

Resistant crops

Bell pepper

Broccoli (S-MR)

Broccoli (S-MR)*

Cabbage (S-R)

Celery

Carrot

Cabbage

Cauliflower

Chili pepper

Chive

Common bean

Garlic

Cowpea (S-R)

Leeks

Cucumber

Lettuce

Eggplant

Parsley

Garden beet

Thyme

Irish potato

Mustard

Okra

Parsley

Squash (all types)

Sweet basil

Tomato

Watermelon

*Crop has been reported susceptible or resistant and the reaction is likely due to different populations of the nematode or different varieties.


Table 3. Horticultural or fruit crops and their reaction to the guava root-knot nematode

Susceptible crops

Resistant crops

Ajuga

Avocado

Albutilon

Chinaberry

Angelonia

Citrus

Banana

Croton

Bottlebrush

Eucalyptus

Brugmansia

Evening primrose

Butterfly bush

Firespike

Caladium

Hyacinth bean

Candle bush

Mulberry

Cape honeysuckle

Olive

Common ginger

Passion fruit

Crape myrtle

Pineapple

Fig

Pittosporum

Gardenia

Strawberry

Grape

Guava

Heavenly blue morning glory

Hibiscus

Jujube

Lantana

Ligustrum

Liriope

Luffa

Papaya

Pentas

Princess flower

Salvia

Willow

*Crop has been reported susceptible or resistant and the reaction is likely due to different populations of the nematode or different varieties.


Table 4. Weed plants and their reaction to the guava root-knot nematode

Susceptible crops

Resistant crops

American nightshade

Barnyard grass

Bristly hawkbit

Beggarweed

Bull nettle

Coffeeweed

Common purslane

Crabgrass

Cutleaf groundcherry

Evening primrose

Dichondra

Fall panicum

Ground cherry

Johnsongrass

Hairy beggarticks

Showy crotolaria

Hairy crabweed

Yellow foxtail

Morning glory

Pokeweed

Purple nutsedge

Redroot pigweed

Sicklepod

Smooth pigweed

Spiny amaranth

Three-lobed morning glory

Velevetleaf

Wild cucumber

Wild mustard

Wild ponsettia

Yellow nutsedge







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