Intercropping field vegetables with other species such as clovers shows insect pest suppression which may make chemical control unnecessary. Examples are given to illustrate these effects and the underlying mechanisms are discussed. Intercropping fits into environmentally acceptable and sustainable vegetable‐producing practices. Both economic and ecological conditions must be fulfilled before intercropping‐based commercial production methods can be developed.
Intercropping as a method to reduce crop losses is an old technique, especially in the tropics. During 1977 and 1978 intercropping experiments of Brussels sprouts with Spergula arvensis showed a significant pest reducing effect. Mamestra brassicae and Evergestis forficalis populations showed a strong reduction, whereas Pieris rapae did not seem to respond to intercropping. Late cabbage root fly infestation of the sprout buttons was reduced drastically. Brevicoryne brassicae incidence was decreased in dense intercropping plots only. Injury due to caterpillar feeding showed a grading response to intercropping density, as did the total caterpillar populations. Log dose − effect regression lines allow a comparison of various intercropping densities with other control methods on insect pest population reducing potential.
ZUSAMMENFASSUNG
WIRKUNGEN VON ZWISCHENKULTUREN MIT SPERGULA ARVENSIS AUF SCHÄDLINGEN VON ROSENKOHL
Durch Untersaaten können Ertragsverluste an Kulturpflanzen reduziert werden. Das ist ein altes, bewährtes Verfahren, besonders in den Tropen. Die Einsaat von Spergula arvensis in Rosenkohlbeständen führte in 2‐jährigen Untersuchungen zur signifikanten Verringerung des Schädlingsbefalls. Während die Populationen von Mamestra brassicae und Evergestis forficalis stark zurückgingen, blieb die von Pieris rapae unbeeinflusst. Eine Abnahme von Brevicoryne brassicae konnte nur in Parzellen mit hohen Spergula‐Dichten festgestellt werden. Die Abundanz der Raupen sowie die Beschädigungsintensität durch diese, zeigten eine Abhängigkeit von der Untersaatdichte. Die Regressionsgerade Untersaatdichte zur Effektivität erlaubt einen Vergleich verschiedener Spergula‐Dichten mit anderen Methoden, die das Schädlingspotential reduzieren.
During two consecutive years the effects of intercropping fresh market white cabbage with two species of clover on pest populations and yield were studied. White cabbage cv. Minicole was intercropped with Trifolium repens (white clover) and Trifolium subterraneum (subterranean clover) as compared to the monocrop. During the season observations were made on pest population developments, especially of Mamestra brassicae L. (cabbage moth), Brevicoryne brassicae L. (cabbage aphid), Delia brassicae L. (cabbage root fly), and evaluation of caterpillar feeding injury. At harvest the yield in quantity and quality was determined to be able to assess the gross financial result. Intercropping effects in terms of suppression of oviposition and larval populations of various pests were found. Although no pesticides were used and competition reduced the weight, the quality of the intercropped cabbages lead to a better financial result compared to the monocropped cabbage crop. The results are discussed in the perspective of the practical implications in the context of IPM.
The speed of development and food consumption of four lepidopterous pest species of cabbage crops were determined, namely Mamestra brassicae L. (Noctuidae), Pieris rapae L., Pieris brassicae L. (Pieridae) and Evergestis forficalis L. (Pyralidae). The relative feeding capacity of these species as a variable in yield loss equations in crop loss assessment was established and discussed.
Zusammenfassung
Frasskapazität von Raupen an Kohl, ein Faktor im Bewertung von Ertragsverlust
Für die vier Kohlschädlinge (Lepidoptera: Mamestra brassicae, Pieris rapae, Pieris brassicae und Evergestis forficalis) wurden Entwicklungsgeschwindigkeit und Fraßmenge ermittelt. Die relative Fraßkapazität dieser Arten wird als Variable in Ertragsverlustgleichungen verwendet und deren Nutzanwendung diskutiert.
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