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SUMMARYThe efficacy of diatomaceous earth (DE) formulations against insect pests is greatly influenced by environmental conditions. It is effective only under dry conditions and becomes wholly ineffective if it is wet. High air relative humidity and especially rain greatly reduce or completely destroy the efficacy of DE when used outdoors. Furthermore, depending on the insect species and commodity treated, DE takes from one to several days to kill insects, even in a dry environment. Because of these factors, DE is in limited use outdoors, especially in regions with a high precipitation. The main uses of DE are for the protection of stored agricultural products against insect infestation, in food industry for structural treatment and for indoor use against some household insects living in a dry environment. The mode of DEs action against insects, the effect of humidity and moisture on DE efficacy, brief overview of the research of DE use in stored grain protection and attempts to overcome DE limitations with combined use of DE and other reduced-risk methods with the insecticide activity for direct mixing with grains are discussed in this article.

Laboratory bioassay was carried out to study the insecticidal effect of 9 Croatian inert dusts against Sitophilus oryzae (L.) and to test their influence on bulk density of treated wheat. In order to compare effectiveness of Croatian inert dust samples, a standard USA diatomaceous earth (DE) Celatom® Mn 51, registered as an insecticide for stored-products protection, was used. Wheat kernels with approximately 13% moisture content were treated with inert dusts at doses 300, 400, 500 and 600 ppm and mortality of S. oryzae adults was assessed after 7 and 14 days and progeny after 49 days. The most effective Croatian inert dust samples were D-02B, D-01 and MA-4 with the LD90 values of 359.6, 447.2 and 458.7 ppm, respectively. In addition, effective dose that reduced F1 progeny in half was lower in regard to the other tested samples including the standard DE Mn 51, with the ED50 values 71.9, 54.6 and 137.6 ppm, respectively. According to the XRF analytical results, the highest amount of biogenic silica (BSi) was found in samples D-02B, D-01 and MA-4 (45.98, 35.09 and 21.28%, respectively). Paleontological data analysis confirmed diatoms species in only 5 samples of Croatian inert dusts (D-01, D-02B, PD-1, MA-4 and JU-1). All tested inert dusts affected reduction in bulk density of treated wheat at the LD90 concentrations, from 4.4 (D-02B) to 5.6 (JU-1) kg hL-1. More effective inert dusts at lower doses equally reduced bulk density as less effective inert dusts at much higher doses.

Laboratory tests on insecticidal effectiveness of disodium octaborate tetrahydrate, diatomaceous earth and amorphous silica gel against Sitophilus oryzae (L.) and their effect on wheat bulk densityLaboratorijska testiranja insekticidne učinkovitosti dinatrijevog oktaborat tetrahidrata, dijatomejske zemlje i amorfnoga silika gela na Sitophilus oryzae (L.) te njihov utjecaj na hektolitarsku masu pšenice Korunić, Z., Rozman, V., Liška, A., Lucić, P. Original scientific paper Izvorni znanstveni članak SUMMARY We examined insecticide effectiveness of three different inert dusts: disodium octaborate tetrahydrate (DOT) and diatomaceous earth (DE) Celatom ® Mn 51 applied as powder and suspension, and silica gel Sipernat® 50 S applied as powder against Sitophilus oryzae (L.) and their reduction of grain bulk density. Sipernat ® 50 S was the most effective dust with a very fast initial effectiveness. DE and DOT generated similar effectiveness against S. oryzae. DOT generated low initial effectiveness but after prolonged exposure time of 8 and especially after 21 days, the mortality was very high (100%), similar to the effectiveness of DE. The similar order of dusts was obtained in the reduction of wheat bulk density. Applied at dose of 200 and 500 ppm, the lowest bulk density difference in regard to bulk density of untreated wheat had DOT (-1.1 and -1.9 kg hl -1 , respectively), followed by Celatom ® Mn 51 (-3.5 and -4.3 kg hl -1 , respectively) and Sipernat ® 50 S (-5.2 and -5.5 kg hl -1 , respectively). Due to the effect on wheat bulk density DOT belongs to the group with the least negative effect on bulk density and therefore, it is a promising dust to control stored grain insect pests.

The aim of the study was to determine the influence of different methods on breaking seed dormancy of weed species velvetleaf (Abutilon theophrasti Medik.) and redroot pigweed (Amaranthus retroflexus L.). The influence of seed sowing depth on emergence and growth of weeds was also evaluated. The results showed that the best treatment for breaking seed dormancy of velvetleaf was immersion of seeds in hot water (60°C) for 1 hour, while immersion in distilled water and 0.2% KNO 3 solution had no significant effect. Seed germination of redroot pigweed was significantly increased in all treatments, however 2% KNO 3 solution and cold stratification at 5ºC for 12 days had the greatest effect. Treatments had different influence on mean germination time, seed germination dynamics and seedling length of weeds. The highest percentage of emerged velvetleaf seedlings was recorded when seeds were sown at 1 to 4 cm depths and ranged from 55.6 to 67.9%. With the increase of sowing depth the emergence percentage decreased, however one quarter and one fifth of the seedlings emerged from 7 and 9 cm depths. Both seedling length and fresh weight were greater at lower sowing depths. Emergence of redroot pigweed was not significantly influenced by sowing depth, however seedlings length and fresh weight were greater at 5 cm depth than at 1 cm.