Assessing organic mulches for thrips control in avocado orchards


This project has four objectives: (1) Determine if autoclave-excludable factors in composted organic yard waste (mulch) are responsible for suppressing avocado thrips pupation rates beneath avocado trees. (2) Determine if humidity and temperature influence avocado thrips survival rates in autoclaved mulch. (3) Evaluate the mortality caused by individual natural enemy species (e.g., micro-athropods, fungi, and nematodes) extracted from mulch on thrips pupation rates when re-introduced into autoclaved mulch. (4) Determine if guilds of extractable natural enemies are more efficacious than individual species for killing thrips pupae in autoclaved mulch.

Preliminary work has indicated that composted mulches below avocado trees significantly reduce thrips pupation rates in comparison to non-mulched plots. The mulch we have been testing for thrips control has been demonstrated to suppress avocado root rot (Phytophthora cinnamomi) because of the presence of antagonistic micro-organisms that flourish in mulches. Additional benefits of applying organic mulches in orchards include: increased water conservation, improved soil fertility and weed control. As a result, use of mulches can increase yields of avocado fruit by up to 13%. The work we propose here will enhance our understanding of suppressive mechanisms in composted mulch that reduce avocado thrips pupation rates.

Abiotic factors such as humidity or temperature may effect thrips pupation rates in the mulch, while biotic factors such as generalist predatory micro-arthropods, entomopathogenic fungi, or entomopathogenic nematodes may contribute to thrips mortality. Abiotic and biotic mortality factors will both be evaluated in the laboratory using field collected second instar avocado thrips larvae (this pest is inordinately difficult to maintain in culture). Identification of efficacious natural enemies amendable to mass-rearing may provide a suite of individual biological control agents, or even a controlled mixture of these agents in a more resilient “biological control community”, which may be used to amend mulches prior to their being laid in orchards for thrips control.

Sources of support


July 1st 2002 - June 30th 2004

Project team


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