Krenite herbicide appears suitable for controlling invasive birch Betula spp. on lowland heathlands in southern England


Heaths in England are prone to shrub and tree invasion, birch (Betula pendula and B.pubescens) being particularly invasive. Birch is difficult to remove by cutting alone as it resprouts vigerously. The effects of a recently available herbicide, Krenite (active ingredient fosamine ammonium), on birch, bracken Pteridium aquilinum (another native invasive) and ground flora, were assessed on lowland heather Calluna vulgaris heaths in southern England.

In two experiments (1 and 2), Krenite was applied (by mist blower) at the maximum recommended rate of 10 litres/ha (4.8 kg a.i./ha) in water (300 litres/ha) with a wetting agent (0.25% Agral). At Woolmer Forest a 1% Krenite solution (0.48% a.i.) was used.
Experiment 1: Cavenham Heath National Nature Reserve, Suffolk (OS grid ref. TM 755694). Three blocks comprising two (20 x 10 m) plots were delineated; one plot in each block was sprayed on 28 August 1980. In 1981 and 1982 birch tree heights were remeasured and herbicide effects recorded. New birch seedlings were counted and any visible damage in Calluna vegetation recorded in sample quadrats.
Experiment 2: Knettishall Heath, Suffolk (OS grid ref. TL 985805). In January 1980, four blocks each with four plots (10 × 5 m) were established in Calluna being invading by birch and bracken. Four treatments were applied:
1. No treatment (control);
2. 2,4,5-T (in diesel) applied by paintbrush to cut stumps, January 1980;
3. Sprayed with Krenite, August 1980;
4. Treatment 2 followed by 3.
Monitoring was undertaken in the July of 1980, 1981 and 1982.
Experiment 3: Woolmer forest, Surrey (OS grid ref. SU 790327). Heathland around a poolhad been invaded by birch and willow Salix spp. A 70 × 50 m area was treated with Krenite in September 1981. The scrub was cut and removed in autumn/winter 1982-83. Vegetation monitoring was undertaken in summer 1982 and 1983 in five (10 × 10 m) permanent quadrats.

Experiment 1: Krenite resulted in trees losing their foliage soon after application. By the next summer, 90% of treated birches were dead. Birch seedling colonization increased in treated plots. Some minor damage to Calluna occurred in both untreated and treated areas (the latter more so) but recovered during 1982.
Experiment 2: Stump treatments and Krenite alone produced good birch kills (>90%).Krenite reduced the number of bracken fronds by an average of 196/plot in
1981 but increased in 1982 to greater than pre-treatment levels, although still fewer than in untreated plots.
Experiment 3: Krenite produced a good kill of birch, only a little Calluna damage was noted. After initial success, much willow had regenerated by 1983. Krenite overall appears suitable for birch control on lowland heaths.
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