Black Spots on Watermelon Leaves Could Be Several Different Insects

Q. I have attempted to grow watermelons for the first time last
summer and everything was looking good until it got hot. These tiny black
specks appeared on the back of some of the leaves.  I was told it was aphids but they weren’t
sure.  I hope you can see them clearly
from the picture I’ve attached. Should I use insecticidal soap as recommended or
something else? 

A. I tried to magnify the picture so I could see the black
spots better. I was curious if these were in fact from insects or not. I could
not see it clearly but whatever it was, it appeared that it was no longer a
problem and the leaves seemed nice and healthy.

            Aphids are
cool weather insects and so when the heat hit they should have disappeared. The
big insect problems for you on watermelon would be aphids earlier in the season
during cool weather, squash bugs shortly after planting and whiteflies (during
the heat).

            Yellow
sticky traps can provide a method to determine if whiteflies are a problem or
not. I will post a short video on my blog on how to make these rather than buy
them. They are handy to place in the garden for insect monitoring.

            Soap and
water sprays are good but must be done about every three or four days and the
underside of the leaves must be sprayed as well. Squash bugs are nasty and can
be vacuumed or hand-picked or delay planting by seed until after June 1. If you
are hand picking or vacuuming squash bugs then be diligent for about three or
four weeks and keeping the plants cleaned off every couple of days by hand
until mid-June to avoid most of the problems with this insect.