When pine needles turn reddish-brown in early summer, several things could be the cause. It could be beetles in the trunk, compaction damage to the roots or, occasionally, a needle disease.
In the year after a wet summer, the disease called ‘needle cast’ may cause numerous pine trees to become ‘red-topped.’
Usually it is the interior needles that are affected. The new needles on the tips of the branch remain green. This is because the disease infected older needles during wet weather the previous summer. Young needles of the current year are not yet infected, since sporulation occurs on late summer.
If the current summer is dry, needle cast disease is halted and the pine recovers. If the current summer is wet, the disease may become severe enough to kill young pines.
According to Dr. Jean Williams-Woodward, “The most likely cause of this needle cast is the fungus, Lophodermella cerina, cause of Lophodermella needle cast. The fungus produces spores on the infected one-yr-old needles that are then spread to the current year’s growth in late summer.
Needle cast diseases are typically controlled by chlorothalonil (Daconil, Bravo, etc). Bayleton (triadimefon), Cleary’s 3336 (thiophanate methyl), and Banner Maxx (propiconazole) are also labeled for control. Applications, if desired, should begin in about early July to protect the fully expanded current year’s growth.”