Crop Report – June 15, 2022

Soybean Update

Soybeans range from VE (emergence) to the fourth trifoliate leaf stage. The majority of the crop was planted in May, although sporadic showers meant that some could not be planted until June. A few soybeans were planted in April. They are now at the fifth trifoliate leaf stage. Ideally, soybeans should have 6 trifoliates by the time they begin to flower to maximize yield potential.

What is the Critical Weed Free Period?

Soybeans are susceptible to yield losses from weed competition, especially when they are small. The critical weed free period is the time during the growing season when uncontrolled weeds cause the greatest yield loss. Yield losses from the presence of living weeds during this time are irreversible. This makes early season weed control essential.

There are several factors that dictate the exact length of the critical weed free period, such as weed density, weed species, and when the weeds emerge. It’s well documented that if weeds are not controlled by the first trifoliate, yields will decline rapidly each day they are not sprayed. Studies have shown that beginning from the first trifoliate, uncontrolled weeds can reduce yield by 0.5 to 2 bu per acre per day. The first trifoliate to the third trifoliate growth stage is considered the “critical weed free period” since the presence of weeds during this time causes the highest yield losses. In wide rows or low plant populations, the weed free period is slightly longer.

The best strategy to reduce yield losses is to always start with a clean field at planting, either through tillage or an herbicide application. It’s important to know that weeds that emerge at the same time as the crop cause the greatest amount of competition and yield reduction, which is partly why many growers use a soil applied residual herbicide in addition to Roundup. Later emerging weeds have less of an impact on final yield. As a rule of thumb, the first in crop application should be made approximately 21-28 days after seeding.

Is it Too Late to Apply Potash?

Potassuim (K) and Manganese (Mn) deficiency are already evident this year. These two nutrient deficiencies have unique leaf symptoms. K deficient leaves turn yellow along the leaf margins (see Figure 1.), while Mn deficient leaves turn yellow across the whole leaf, except for the veins which remain green (see Figure 2.).

A soil test is the only reliable way to know if a field is truly low in K or if the plants are just showing stress-induced potassium deficiencies. K deficiency symptoms may also indicate soybean cyst nematode (SCN) feeding on the roots. If the soil test is poor for K (less than 100 ppm) a broadcast application at this time is still warranted as a remedial management strategy. Soybeans are very responsive to potash and have the ability to utilize surface applied potash even after planting.

Manganese Deficiency

One of the most significant factors affecting the availability of Mn is the soil pH. As soil pH increases, less Mn is available to the plant. The deficiency is most common on poorly drained soils, especially clays. The amount of air in the soil also impacts available Mn, so tire tracks often show less Mn deficiency. High organic matter also ties up Mn. Since Mn is a micronutrient, a foliar application of Mn works well to rectify the deficiency and can provide a 5+ yield response.

Replants

Many soybean fields are struggling this year to achieve a perfect stand. Keeping an existing stand is often more profitable than replanting at this date. The uniformity of the existing crop is more important than having a high population. Soybeans have an impressive ability to compensate for thin stands under good growing conditions. Soybean plants can fill spaces up to 30 cm (12 inches) within or between rows with relatively little yield reduction. Research has shown that a final stand of 90 000 plants per acre in 7.5-inch rows provides a yield potential of 90%. Plants must be healthy, evenly distributed and weed free for low populations to flourish. Field experience has shown that more plants per acre are needed on clay soils. A minimum stand of about 110 000 plants/acre on heavy clay soils is required to achieve good yields. When thickening a poor stand, use the same variety. These later planted seeds will mature within 10 days of the original stand even though they may have been seeded a month later in the spring.

Weather Data – June 6 – 12, 2022

Location	Year	Highest Temp (°C)	Lowest Temp (°C)	Rain (mm)	Rain (mm) April 1st	GDD 0C April 1st	GDD 5C April 1st	CHU May 1st
Harrow	2022	27.4	11.4	33.1	189	924	592	844
	2021	29.8	12.8	6.3	130	956	610	772
	10 YR Avg. (2011-20)	25.9	12.1	15.7	218	923	561	822
Ridgetown	2022	25.9	9.3	42.1	170	859	534	765
	2021	29.2	11.1	7.1	122	897	559	740
	10 YR Avg. (2011-20)	25.6	11.0	9.1	188	855	497	755
London	2022	24.5	8.1	30.2	181	833	513	733
	2021	30.4	12.6	7.8	127	898	565	717
	10 YR Avg. (2011-20)	25.2	10.3	18.6	208	837	483	742
Brantford	2022	25.0	7.8	31.5	161	827	501	706
	2021	31.8	13.4	4.8	120	872	538	702
Welland	2022	26.2	10.1	41.0	186	876	540	758
	2021	29.7	14.5	3.0	85	866	527	686
	10 YR Avg. (2011-20)	25.0	9.8	20.8	216	838	483	736
Elora	2022	23.9	7.9	38.3	163	761	448	648
	2021	31.3	12.3	3.3	97	793	468	628
	10 YR Avg. (2011-20)	24.0	8.7	20.4	208	731	390	637
Mount Forest	2022	23.7	8.3	46.3	179	768	461	672
	2021	30.4	12.0	2.7	100	806	483	643
	10 YR Avg. (2011-20)	24.2	8.7	22.4	193	716	383	631
Peterborough	2022	22.9	6.9	80.6	199	769	441	672
	2021	30.6	8.6	1.0	91	784	448	622
	10 YR Avg. (2011-20)	24.7	7.8	26.2	201	744	403	652
Kemptville	2022	24.0	7.3	29.2	271	845	497	741
	2021	32.0	9.6	0.6	98	888	545	693
	10 YR Avg. (2011-20)	24.9	9.3	25.0	204	779	439	690
Earlton	2022	23.7	6.2	30.5	144	660	381	632
	2021	33.7	5.2	1.2	79	744	428	584
	10 YR Avg. (2011-20)	23.4	6.2	15.7	162	543	286	516
Sudbury	2022	23.1	7.9	46.2	184	658	371	604
	2021	31.6	9.7	23.2	120	743	428	586
	10 YR Avg. (2011-20)	23.2	8.0	12.7	185	601	322	557
Thunder Bay	2022	25.1	3.1	4.3	302	482	231	427
	2021	31.5	4.1	29.8	185	615	312	511
	10 YR Avg. (2011-20)	22.3	5.2	12.7	164	491	222	426
Fort Frances	2022	24.1	2.4	2.9	301	516	267	492
	2021	32.1	3.9	30.8	142	684	375	614
	10 YR Avg. (2011-20)	24.0	6.3	29.6	162	575	289	525