What harm does alligator weed cause, and how should it be controlled?

In summer, on the surface of ponds, we can often see a full blanket of green dotted with small white balls, which are the flower heads of alligator weed. Alligator weed is already distributed across most of China, causing severe invasion in the southeastern region. So what are the main harms of alligator weed? What control methods are there?

1. What are the main harms of alligator weed?

1. It covers water surfaces, blocks navigation channels, and affects human water-based economic activities;

2. It invades urban green spaces such as parks and lawns, damages garden landscapes, and increases maintenance costs;

3. It harms farmland and reduces crop yields;

4. It breeds mosquitoes and flies, and often carries harmful parasites, endangering human and livestock health;

5. It has strong reproductive capacity, crowds out other plants, reduces the stability of plant communities, and damages the ecological environment.

Alligator weed spreads extremely easily. Its stem is hollow, brittle, and breaks easily; often a single plant fragment or stem node can become a new source of infection, and when its storage roots are disturbed or stimulated, they can produce large numbers of adventitious roots and buds, so it spreads very easily with human activity. Genetic studies show that the alligator weed widely distributed in China spread in large quantities over a short period after invasion, and its population genetic diversity is very low, possibly the clonal offspring of the same clone.

2. What control methods are there for alligator weed?

Alligator weed can thrive both in water and on land, which is inseparable from its variable physiological characteristics. In water bodies, alligator weed grows semi-upright and creeping, its roots can attach to the mud along the banks, and its stems have relatively large hollow cavities, creating greater buoyancy so it can float on the water surface; this is where the word “hollow” comes from. When living on dry land, alligator weed grows in a creeping state, spreading continuously by means of adventitious roots produced at the nodes, and it also develops specialized storage roots nearly 1 cm thick and more than one meter long, with root hairs; the plant height is generally 30 cm and the stems are firm. Its stem nodes, thick root parts, and underground roots can all grow and spread through fragments. If we see, on a lawn, mudflat, or water surface, a large patch of plants with long oval opposite leaves dotted with small white spherical flower heads, then nine times out of ten it is alligator weed. The alligator weed flea beetle has poor control effects on the terrestrial form of alligator weed, so at present control is still mainly carried out by manual and mechanical removal and chemical herbicide spraying.

1. Biological control

When the minimum temperature in early spring rises back above 10°C, release adult alligator weed flea beetles, at 1000-3000 adults per hectare of water area, which can control their harm and spread. However, using the specialized predatory natural enemy insect Agasicles hygrophila, native to South America, gives better control of aquatic-type plants but poor results against terrestrial types.

2. Agricultural measures

Strengthen field management at ordinary times; do not farm roughly, but cultivate intensively and carefully. During the seedling stage of alligator weed, repeatedly and carefully pull it out and clean it up, dig out the residual stem nodes in the soil, and gather them to dry in the sun and burn. Areas where alligator weed has not yet been found should strengthen prevention to keep its asexual reproductive bodies from invading fields, pastures, or water areas. In areas where it has already occurred, measures should be taken to control its spread.

3. Physical control

Use manual and mechanical removal and salvage; when removing and salvaging alligator weed, dig as deep as possible or salvage it together with the roots. The removed and salvaged alligator weed can be gathered and burned or fully composted into green manure for use. In addition, when the effect of chemical control is not ideal, part of the alligator weed can first be salvaged and removed to reduce the population density of alligator weed, and then the pesticide can be sprayed.