Pest Management

Late this past winter, as daffodil leaves of early varieties emerged, I observed an area in one bed where the leaf shoots were misshapen and some shoots were simply missing. I dug a sample of bulbs and took them to the Contra Costa County Agricultural Office.  They forwarded the bulbs to the California State Agricultural Laboratory, where microscopic analysis diagnosed Cobb’s lesion nematode (pratylenchus penetrans).

Before construction of my home and the 0ther tract homes on neighboring lots, the property for decades had been an almond orchard. This nematode is a major pest for stone-fruit trees.  So, it is thought that the nematode came with the property! This nematode is also a major problem impacting lily growers in Humboldt County, along the northern coast of California.

The Contra County County Agriculture Office had not addressed issues of pests in ornamental plants, only of vegetables and fruit. (I live in a major agriculture and orchard area.)  Because I was hybridizing plants for possible introduction into the horticultural trade, the Ag Office has decided to make my situation their introduction. They are working up a comprehensive pest-management plan for my daffodil patch. The purposes are to (1) to prevent or minimize the spread of the nematode from the infected area, and (2) to control/manage the incidence in the infected area.

I “rotate” growing in my patch to the extent feasible for me. That means that one-third of the patch is dug at the end of the growing season (in early June), and left fallow until planting time the next year (in November). That leaves the area fallow for about 17 months.

I have embarked on the preliminary portion of the Management Plan. That  is using solar sterilization on half of the area that has been fallow since last year and is due for planting in November 2012. The unsterilized part of the area will serve as a comparison area during the coming growing season. The portion dug in June 2012 and to be replanted in Fall 2013 has been left fallow – with no covering.

It is thought that solar sterilization offers some mitigation – but not elimination – of nematodes. It kills those near the surface and drives survivors deeper in the soil, and thus delays their impact. When plant roots grow deeply, the nematodes are there to enter the plant through them.  There is a side beneficial effect in that basal-rot fungus is killed by solar sterilization.

The entire plan will deal with both areas of the patch currently empty of bulbs. Foliar applications and other methods are to be applied.  Control areas will be established so any results might be observed. The entire daffodil patch is not large (50′ x 35′), so I’m somewhat dubious  that meaningful conclusions can be reached about the effectiveness of various treatments. However, if the outcome is the restriction of the nematodes to the small area  of infection, it will be successful.