Blossom end rot is caused by several environmental conditions. If there is too much rain the squash may not be able to develop properly as the fine root hairs suffer in water logged soil. If there is lack of moisture in the soil at this crucial time the ends of the squash will rot as well. A mulch on top of the soil will help to keep the moisture more consistent. Another cause is lack of calcium most often caused by a high nitrogen fertilizer. When the squash takes up too much nitrogen this hinders the uptake of calcium - so do not over feed. Using a slow release plant food like Osmocote will help avoid over feeding. One last cause of blossom end rot is over cultivation of the soil such as hoeing or raking near the plants. This may damage the fine hair roots of the squash plants and when the roots suffer the tips of the squash stop developing. Once again keeping a mulch around the roots will help protect them from damage. Don't give up, there is still time to address the problem and your squash plants can go on to produce plenty of harvest this summer. Keep growing, Marianne Binetti