The litte dockcock
In the Netherlands there exist two sorts of leafbeetles, namely the Green Dockcock(G. Polygoni) and the Twocoloured Dockcock(Gastrophysa viridula). The first one is about 4-6 mm long and goldcoloured-green. The second one is something smaller, darkblue till greenlike of colour and has a red neckshield.
Both sort of beetles overwinters as imago(adult) in the soil near the attacked plants on a depth of 5-15 cm. In the first half of may they are coming present in the open. The eggs are placed on the underside of the leaves. The Green Dockcock can produce at a optimum-temperature of 15o C 100-1000 little eggs pro little wive.
The Twocoloured Dockcock brings at an optimal temperature of 25o C about 400-700 eggs. Usually there are two generations pro year. The larvea and beetles eat, big, irregularley holes in the leaves. This leafdamage leads never till real damage.
Beetcystennematodes(Heterodera Schachtii - white beetcystennematode and Heterodera trifolii Goffart f.sp. betayellowbeetcystennematode)
Often appears here lokaly bad growth; sometimes even stunning growth on the whole parcel, together with a huge reduction of the production. The rootsystem is sometimes bearded and on the roots are the cysten.
Treatment: No cultaving beets, beetroots, spinach(summer-and autumnculture), cabbage, swedish turnip and rhubarb as a pre-crop.
Stalknematodes (Ditylenchus dipsaci) and Destructornematode(Ditylenchus destructor)
Namatodes comes from the soil into the plant in the region under the sidebuds, by which there is starting rotting. The underside part of the leafstalks are even attacked. The stalks are pumped up a little bit and the structure makes a dismoulded impression. The plants are falling away at the end. Preventing the attack of nematodes is a question of planting out only healthy young cuttings on a not infected soil. Soil samples on nematodes is the first act on new parcels for rhubarb.