Up to15 years ago, sciarid control was fairly easy. Apply Dimilin at label rate immediately after casing and job done. Today such insecticides are either banned by supermarkets or registration authorities. Furthermore many pests have become resistant to such applications. So things have become more complicated.
In most mushroom producing countries nematodes have now taken over from Dimilin. To get good results, however, you need to know a lot more than previously: You must understand the characteristics of nematodes and the life cycle of sciarids and how all of this fits into your production schedule.
Nematodes are small, but larger than you may think, notably 0.6 mm in length. To avoid stressing the nematodes, all irrigation openings where the nematodes shall pass through, must have a width of at least 0.8 mm. Filters and sieves can block nematodes and thus should be removed prior to application.
Nematodes live and infest for at least 6 weeks. During their development in the fermenter they’ve built up enough fat reserves to live without food. Yet when applied to the casing or compost their numbers reduce quickly; they get washed into deeper compost layers and are eaten up by natural enemies causing a 50 % decrease within one week of application. Therefore nematodes should only be applied, when sciarid larvae are present.
Sciarid eggs develop into new adults within three weeks. During the first 5 days of this cycle, nematodes cannot enter, because the larvae are too small. And during last 5 days of this cycle, nematodes cannot enter, because the larvae have transformed into pupae. Out of 20 days of development time, nematodes can only enter during 10 days. What does this mean for the application timing?
On a phase II farm eggs are laid in the freshly spawned compost. At casing these eggs have developed into mature larvae close to pupation. A small dose of 1 million nematodes per m2 at casing comes at the right moment and will produce fresh nematodes through recycling within 10 days. However, new flies come in at casing and lay eggs again. A second application with last watering at a rate of 1-2 million per m2 is necessary because the nematodes must survive a few days until the larvae are large enough to enter.
On a phase III farm we consider the compost to be free of sciarids. At casing flies enter the tunnels and lay eggs and 5 days later larvae are large enough for the nematodes to enter. That is when our 10 day window of application starts. Growers who do not water any more at this time have two options:
First, follow the recommendation for phase II farms but apply 1.5 million nematodes at each application. This ensures that a sufficient number of nematodes survive into the effective period. Never apply less than 1 million nematodes per m2 per single dose, this would not be effective.
Secondly or alternatively, apply a full dose of 2 million right in the application window between day 10 and day 15 after casing. Use as little water as possible, 1 litre per m2 or less, just enough to get the nematodes evenly distributed over the casing. With this application the larvae are targeted when they are most susceptible. Nematodes that multiply in these larvae will protect the crop through the second and third flush.
For further information or any question specific to your farm, please feel free to write to m.barth@e-nema.de
