Ssquash Yllowing Laves‏

Folks,

Sending to all as an FYI

RE: yellowing squash leaves
Did some Googling and came up with the following:  (Please read to the note's end message)

1. Squash vine borer is a difficult to control pest of vine crops, particularly summer and winter squashes.  Adults lay eggs for a three week period starting in late June.  Cover lower section of stems with floating row cover or even aluminum foil to prevent egg laying.  Look for and remove by hand any brown egg masses seen on the lower stems.  Spraying carbaryl (Sevin) is more effective than using the dust formulation.  If entrance holes and "sawdust" are seen, a wire can be inserted and threaded through the stem for some distance to kill developing larvae inside. Or slit stems lengthwise to find and destroy the caterpillar. Then bury slit stem section under some soil. (852)
2. Yellow leaves are generally a sign of over-watering.
   
   Pluck off the yellow leaves close to the stalk, to prevent mold.
   Stick your finger in the soil about an inch or two away from the plant.
   If you can feel moisture, don't water it. Check it again the same way the next day. If you still feel moisture, don't water it. If it feels dry, water a little. Try to check the soil this way in the early evening as opposed to morning or night when dew may be present on the ground. Try to avoid watering a plant that is already sitting in wet soil. Roots that are saturated tend to get what's known as "root rot."
   
   Also, (you probably already know this) water in the evening to prevent the water from evaporating from the soil too quickly in the heat of the day. Even with temps in the 70's, there will be evaporation. If you have holes in the middle of the leaves, then that's a sign of bugs. If the leaves are brown, that means it needs more water.
   
   Don't worry, plants are pretty strong. Your squash will be okay, just keep an eye on those little things.
3. If it's the basal leaves turning more yellow than the leaves closer to the shoot tip, then it's a nitrogen deficiency. The plant recycles nitrogen from older leaves and trans-locates the nutrients to the younger leaves.
   
   If all leaves are more yellow away from leaf veins and more green at the vein (interveinal chlorosis) then it is likely an iron or zinc deficiency. This generally occurs in soils with a pH greater than 8.0. If you are in a more arid region of California, maybe less than 16" of rainfall a year, you could have high pH soils.
   
   Because the yellowing started after a rain, I suspect a nitrogen deficiency. Nitrogen is found in several chemical forms in the soil, and bacteria metabolize other forms of nitrogen and oxidize it to Nitrate (NO3). Nitrate is the form of nitrogen taken up by plants in the greatest quantity. Nitrate is negatively charged and does not "stick" to positively charged clay particles in the soil like other nutrients and is easily leached by rainfall below the root zone. Many aquifers agricultural areas are polluted with nitrate because of this reason.
   
   I suggest fish emulsion or feather tea, both of which contain most of their nitrogen in the nitrate form, and will be rapidly available to the plants, unlike a pelletized slow release fertilizer.

So, let's look for sawdust around the lower stem.  If found, we'll look for entry and get the little sucker out.  If none is found, then we'll try some fish emulsion, which I will pick up when I get the spray.

If anyone has further info regarding yellowing leaves, please share with us.
Cathy