microscopic worms may be a reduction in overall growth of any 

 sized-trees but the problem, is most evident in newly planted blocks 

 that fail to develop uniformly. 



The nematode species most often associated with poor growth 

 of apples in the Northeast is the meadow nematode, Pratylenchus 

 penetrans . This parasite is also called the lesion nematode be- 

 cause adults and larvae burrow through the root cortex, breaking 

 down cells and causing tissue collapse. The initial cavities or 

 spots become infection courts for numerous fungi and bacteria which 

 complete the breakdown of the roots. Populations build up fastest 

 in lighter soils, or at least injury seems to be more severe in 

 sandy and sandy loam soils but this is not always the case. 



The other nematode species most often found feeding on apples 

 are ectoparasites, meaning that they remain in the soil. Their 

 surface feeding does not cause extensive tissue breakdown but can 

 contribute to reduced root groivth. 



Poorly developed root systems lead to a variety of symptoms. 

 Water is not absorbed efficiently and trees become stunted. Mar- 

 ginally available nutrients become limited. Poor growth leads to 

 poor winter hardiness. Dagger nematodes, one of the ectoparasitic 

 species, are transmitters of peach viruses and may possibly trans- 

 mit apple viruses as well. 



Experimental evidence that nem.atodes injure apples is usually 

 obtained either by adding nematodes to seedlings growing in pots 

 or else by treating larger trees with chemicals called nematicides 

 and comparing them with untreated trees. A number of general con- 

 clusions may be drawn from the research literature in the U.S. and 

 Europe. 



1. The presence of nematodes does not always mean that chem- 

 ical treatment will lead to increased yields. Healthy trees, grow- 

 ing vigorously, can support relatively large numbers of nematodes 

 and are unlikely to grow better with treatment. 



2. Treatment is usually profitable only when there is evidence 

 of poor root growth or reason to suspect that there might be. Soil 

 should be sampled and analyzed for nematodes but at the same time, 

 nutrient levels, drainage, hardpan and other soil conditions should 

 be checked out. 



3. The younger the trees, the better the chances for success 

 from chemical treatments and for all practical purposes, nematode 

 control should be done in conjunction with planting. It is far 

 easier to prevent infection than to try and get rid of nematodes 

 already in the roots. 



4. The head start given to young trees will usually last for 

 the life of the tree even when nematode populations build up later. 



