small tomato plants in greenhouse
Sometimes this can be due to lack of nutrition (in addition to symptoms on older leaves, young leaves are starting to come out yellow or white). A simple way to check this out is to water it with a fertilizer solution and look for response in 48-72 hours. If younger leaves appear to green up and new leaves appear normal, then you have found and solved the problem.
If you are seeing white spots then it may be thrip damage with the pest probably coming from the greenhouse. Plants will probably outgrow once the weather warms. You can spray the underside of the plants to remedy.
One other common cause of white areas on leaf tips or whole leaves at this time of the year is cold or frost damage. The plant may recover from such damage, but if the damage is severe the plants will not survive, or take too long to recover. If the plants don’t improve then I would suggest taking one of the plants to your locale extension office in Venango County located at 867 Mercer Road
Franklin, PA 16323 Phone: 814-437-7607
VenangoExt@psu.edu Office Hours Monday-Friday 8:30 a.m. - 4:30 p.m.