DOWNY MILDEW 
The disease appeared first in this country about 1890, being observed in New Jersey. It attacks Cucumbers 
and Muskmelons most seriously, being less severe on Squash, Pumpkin, and Watermelons. All varieties of 
each host are about equally susceptible. 
SYMPTONS: 
It appears first at the central part of the plant in the fonn of irregular yellowish spots on the upper side of 
the leaves. If the under side of the leaf is examined when moisture is present the lesions will show a purplish 
border of fungus growth. The disease spreads rapidly until the whole leaf withers and dies. The plants are de¬ 
foliated until only the ends of the vine remain green bearing partially formed fruit of poor quality. 
CAUSE: 
The fungus is known as Peronoplasmopara cubensis. It fruits the year around in the extreme south and 
finds its way north by easy stages during the warm season. It may also live over the winter in green houses and 
spread to outdoor hosts during warm weather. This disease does not live in the soil and is not seed borne. Its 
growth seems more rapid during rainy periods with cool nights followed by warm days. 
CONTROL: 
Spraying with bordeaux mixture or dusting with copper lime dust will eliminate Downy Mildew. 
ROOT KNOT OR NEMATODES 
Root Knot is becoming increasingly serious in practically all parts of the United States except the northern 
sections. It is everywhere prevalent in greenhouses. The Nema affects all cucurbits about equally. It causes a 
dwarfing of the plant which wilts readily in hot, dry weather and is usually of a pale green color. The plants 
may be killed entirely under severe conditions. 
CAUSES: 
The parasite is known as Heterodera radicicola, a minute worm-like creature that bores into the root near the 
tip. It feeds on nourishment from the root irritating the tissues in such a way, that knots of considerable size are 
formed. In the warmer climates it is not uncommon for ten or twelve generations to appear in one year. One 
female may hatch as many as 500 eggs per season. 
CONTROL: 
Crop rotation is the most satisfactory method of control, especially with immune crops. Also the fields 
must be kept entirely free from weeds. Frequent change of crops is helpful to prevent the nemas from adapting 
themselves to any certain host plant. Steam heat can be used to overcome the trouble in the greenhouse. 
CURLY TOP 
Curly Top is a disease more generally associated with sugar beets. However, in some sections it has become 
serious among cucurbits and many other garden vegetables. Squash, Pumpkin, Cucumber and sometimes Musk- 
melon are attacked. Stunting of the plants is characteristic of the disease on all hosts. The symptons appear 
only at the ends of the vine, the shortened runners presenting a rosetted appearance. 
CAUSE: 
Curly Top is due to a virus which is carried over winter and spread by a sucking insect, the beet leaf hopper, 
Eutettix tenellus. The insects migrate long distances from their breeding grounds and their spread is very rapid. 
CONTROL: 
Control measures for this insect have not proven effective. The most promising methods seem to be the pro¬ 
duction of only those kinds which are resistant. Experiments and breeding work are now being conducted 
toward this end. Some of the Pumpkins, especially those of the group C. Moschata, have shown marked resist¬ 
ance. Among winter Squash the Yakima Marblehead is recommended for use where curly top is serious. Squash 
of the Vegetable Marrow types also appear resistant to this trouble. 
ONE HUNDRED FORTY-SIX 
