The Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released Jul 10, 2013.

Insect and weed interactions in vegetable crops

By John Palumbo, UA research scientist and Extension specialist

In a recent update, I discussed how sanitation following spring melons is important to prevent whitefly buildups during the summer. With melons now finished, growers are preparing the ground for fall produce crops.

Another sanitation practice - weed management - is very important in preventing insect buildups in fall crops.

Effective weed management is critical for the profitable production of vegetable crops in the Desert Southwest. Weed management is also essential for another important but often overlooked reason.

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Several common weed species found in and around vegetable crops can serve as host plants to many insect pests which can later infest nearby crops. Flowering weeds can provide a reservoir for natural enemies and as a source of nectar and pollen for a pollinators.

These same weedy refuges can serve as host sources for many key insect pests that cause economic damage to vegetable crops.

Weeds found on field margins and ditch banks can provide insect pests with suitable resources for rapid population growth which subsequently can lead to insect infestations occurring in adjacent vegetable crops.

In addition, many weed species can provide insects with host plants which serve as a bridge between cropping seasons when vegetables crops are not in production (i.e. July-August).

Since most key insect pests have the ability to move relatively long distances to find new food sources, weeds which grow unchecked in fallow fields during the summer often serve as a key source of insect infestations for fall vegetable and melon plantings.

For example, pale-striped flea beetle and beet armyworm populations will commonly develop on common purslane allowed to grow in fallow fields prior to fall vegetable and melon plantings.

Volunteer melons and cotton can also be considered weeds (a plant out of place). If not controlled in a timely manner, these weedy volunteer plants can sustain large numbers of insect pests, plus plant viruses transmitted by insect vectors, which can migrate onto newly planted fields.

Finally, weeds can serve as impediments to insecticide applications. Dense weed foliage in vegetable and melon fields can negatively influence foliar spray applications by intercepting spray droplets before reaching the target crop. This can result in less insecticide deposition and unacceptable crop damage.

Soil applied insecticides (e.g., imidacloprid) can also be impacted by unmanaged weed growth. Weeds growing unchecked during stand establishment can compete with seedling plants for water and fertilizer. Weeds can also compete with crop plants for soil insecticides.

Excessive weed densities can significantly intercept insecticides in the soil profile and reduce the amount available for uptake by the target crop.

For more information, please this link: Interactions between Insects and Weeds in Vegetable Crops.

And, click this link to listen to John.

“Remember, when in doubt - scout.”

Contact Palumbo: (928) 782-3836 or