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Impacts Detrimental On rangeland and pastures, whitetop can form dense monocultures (see Fig. 1) similar to other noxious weeds, such as leafy spurge (Euphorbia esula). Noxious weeds displace native plant species, reduce biodiversity, wildlife habitat and forage production and are a serious threat to the cattle and tourism/recreation industries. Yhitetop contains glucosinolates which can be toxic to cattle. In some states, these weeds are problems in small grains, alfalfa, peas, onions, sugar beets and other crops as well as in fallow cropland enrolled in the Conservation Reserve Pmgram. In Montana, whitetop is predominantly found in alfalfa, pas- tures, rangeland and small grain fields. Identification The three species of whitetop are members of the mustard family. The flowers have four petals and six stamens (Figure 2). Individual white flowers (%s-% inch) are borne on slender stalks about a half inch long. Dense blooming stands look very much like a patch of late-melting snow. (Figures 3 and 4) These species can be distinguished from each other by seed pod shape. Globe- podded whitetop has small, purplish, globe-shaped seed pods. The seed pod oflens-podded whitetop is flat and round. Heart-podded has aheart-shaped, broad, flat seed pod. In all species, the seed pod is tipped with a "beak" which is rare for the mustard family. Each pod is oval, reddish brown and a half inch long containing two or four seeds. The plants normally grow from 10 to 24 inches tall. They have both basal and stem leaves. Basal leaves taper to a short stalk that attaches to the crown near the ground. Stem leaves are grayish green, arrowhead shaped, with smooth and occasionally finely toothed edges. All leaves have a covering of soft white hairs. They range from''/s to 3 inches in length and are arranged alternately along the stem. The base of each leaf clasps around the stem at the point of attachment. Life Cycle All three whitetop species are herbaceous, relatively long-lived and rhizoma- tous perennial weeds. They begin their life-cycle in the fall with seed germination and seedling establishment, Occasionally, seeds germinate in the spring. Seed leaves grow very rapidly and lateral roots develop within three weeks. Seedlings overwinter as rosettes. Established plants and first year rosettes initiate growth very early each spring. These species frequently bloom in April and May and begin producing seeds about a month later. After blooming, the plants continue to grow until frost. If conditions remain suitable, they will flower and produce a second crop of seeds late in the summer.