Carrot is a high-value cash crop that is grown in Israel throughout the
year. Egyptian broomrape is a chlorophyll-lacking, obligate, root
holoparasite that parasitizes members of many botanical families, including
the Apiaceae. At high infestation levels, Egyptian broomrape can cause total
yield loss in carrot. A protocol has been developed for the control of
Egyptian broomrape in carrot. Because carrots are grown in Israel under
fall, winter, and spring conditions, information about the relations between
the efficacy of control and temperature is important. Therefore, the
objective of this study was to investigate the response of carrot and
Egyptian broomrape to herbicides at different phenological stages under
varying temperature regimes. This study was conducted under
temperature-controlled conditions in a multiclimate greenhouse and in a net
house. Applications of the imidazolinone herbicides imazapic and imazamox
(each applied at 4.8 g ai ha−1) injured carrot plants and reduced
yield and yield quality. Glyphosate effectively controlled Egyptian
broomrape and did not negatively affect the carrot plants when applied three
times at ≤ 108 g ae ha−1. High temperatures increased the carrot
plants’ sensitivity to glyphosate. This study found that three applications
of glyphosate at 108 g ae ha−1 can prevent Egyptian broomrape
damage without causing any damage to the carrot crop. Our results indicate
that weather conditions can affect herbicide phytotoxicity in carrot. The
highest temperature at the time of herbicide application corresponded to the
strongest observed phytotoxic effect. To summarize, effective Egyptian
broomrape control can be achieved by three sequential foliar applications of
glyphosate (108 g ae ha−1), beginning during the early parasitism
stage (i.e., small tubercles). Moreover, applying glyphosate on carrot at
high temperature (i.e., 28/22 C day/night temperatures) can injure carrot
plants and reduce control efficacy.